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Filed Pursuant to Rule 497
Registration No. 333-214767

This preliminary prospectus supplement relates to an effective registration statement under the Securities Act of 1933, as amended, but is not complete and may be changed. This preliminary prospectus supplement is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED OCTOBER 10, 2017

PRELIMINARY PROSPECTUS SUPPLEMENT

(To prospectus dated September 7, 2017)

$

% Notes due

We are an internally-managed, non-diversified, closed-end investment company that has elected to be regulated as a business development company under the Investment Company Act of 1940, as amended, or the 1940 Act. Our investment objective is to maximize our portfolio’s total return by generating current income from our debt investments and capital appreciation from our warrant and equity-related investments.

We are offering $     in aggregate principal amount of     % notes due       , or the “Notes.” The Notes will mature on      . We will pay interest on the Notes on     and     of each year, beginning on         , 2018. We may redeem the Notes in whole or in part at any time or from time to time, at the redemption price set forth under “Description of Notes and the Offering—Optional Redemption” in this prospectus supplement. In addition, holders of the Notes can require us to repurchase the Notes at 100% of their principal amount upon the occurrence of a Change of Control Repurchase Event (as defined herein). The Notes will be issued in minimum denominations of $2,000 and integral multiples of $1,000 in excess thereof.

The Notes will be our unsecured obligations and rank pari passu, or equally in right of payment, with all outstanding and future unsecured unsubordinated indebtedness issued by Hercules Capital, Inc.

An investment in the Notes involves risks that are described in the “Supplementary Risk Factors ” section beginning on page S-14 in this prospectus supplement and the “Risk Factors” section beginning on page 14 of the accompanying prospectus.

This prospectus supplement and the accompanying prospectus contain important information you should know before investing in the Notes. Please read this prospectus supplement and the accompanying prospectus before investing and keep it for future reference. We file annual, quarterly and current reports, proxy statements and other information about us with the Securities and Exchange Commission, or the SEC. This information is available free of charge by contacting us at 400 Hamilton Avenue, Suite 310, Palo Alto, California 94301, or by telephone by calling collect at (650) 289-3060 or on our website at www.htgc.com. The information on the websites referred to herein is not incorporated by reference into this prospectus supplement or the accompanying prospectus. The SEC also maintains a website at www.sec.gov that contains information about us.

THE NOTES ARE NOT DEPOSITS OR OTHER OBLIGATIONS OF A BANK AND ARE NOT INSURED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Neither the SEC nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Delivery of the Notes in book-entry form only through The Depository Trust Company will be made on or about October     , 2017.

Joint Book-Running Managers

The date of this prospectus supplement is October     , 2017.

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You should rely only on the information contained in this prospectus supplement and the accompanying prospectus. We have not, and the underwriters have not, authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not, and the underwriters are not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information contained in this prospectus supplement and the accompanying prospectus is accurate only as of the date on the front cover of this prospectus supplement or such prospectus, as applicable. Our business, financial condition, results of operations and prospects may have changed since that date.

This document is in two parts. The first part is this prospectus supplement, which describes the terms of this offering and also adds to and updates information contained in the accompanying prospectus. The second part is the accompanying prospectus, which gives more general information and disclosure. To the extent the information contained in this prospectus supplement differs from the information contained in the accompanying prospectus, the information in this prospectus supplement shall control. You should read this prospectus supplement and the accompanying prospectus together with the additional information described under the heading, “Available Information” before investing in our Notes.

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Prospectus Supplement

Prospectus

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FORWARD-LOOKING STATEMENTS

The matters discussed in this prospectus supplement and the accompanying prospectus, as well as in future oral and written statements by management of Hercules Capital, Inc., that are forward-looking statements are based on current management expectations that involve substantial risks and uncertainties which could cause actual results to differ materially from the results expressed in, or implied by, these forward-looking statements. Forward-looking statements relate to future events or our future financial performance. We generally identify forward-looking statements by terminology such as “may,” “will,” “should,” “expects,” “plans,” “anticipates,” “could,” “intends,” “target,” “projects,” “contemplates,” “believes,” “estimates,” “predicts,” “potential” or “continue” or the negative of these terms or other similar expressions. Important assumptions include our ability to originate new investments, achieve certain margins and levels of profitability, the availability of additional capital, and the ability to maintain certain debt to asset ratios. In light of these and other uncertainties, the inclusion of a projection or forward-looking statement in this prospectus should not be regarded as a representation by us that our plans or objectives will be achieved. The forward-looking statements contained in this prospectus supplement and the accompanying prospectus include statements as to:

For a discussion of factors that could cause our actual results to differ from forward-looking statements contained in this prospectus supplement and the accompanying prospectus, please see the discussion under “Supplementary Risk Factors” in this prospectus supplement and “Risk Factors” in the accompanying prospectus. We undertake no obligation to update any forward-looking statement to reflect events or circumstances occurring after the date of this prospectus supplement.

You should not place undue reliance on these forward-looking statements. The forward-looking statements made in this prospectus supplement relate only to events as of the date on which the statements are made and are

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excluded from the safe harbor protection provided by Section 27A of the Securities Act of 1933, as amended, or the Securities Act.

Industry and Market Data

We have compiled certain industry estimates presented in this prospectus supplement and the accompanying prospectus from internally generated information and data. While we believe our estimates are reliable, they have not been verified by any independent sources. The estimates are based on a number of assumptions, including increasing investment in venture capital and private equity-backed companies. Actual results may differ from projections and estimates, and this market may not grow at the rates projected, or at all. If this market fails to grow at projected rates, our business and the market price of our securities, including the Notes, could be materially adversely affected.

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SUPPLEMENTARY RISK FACTORS

Investing in our securities involves a number of significant risks. Before you invest in our securities, you should be aware of various risks, including those described below and those set forth in the accompanying prospectus. You should carefully consider these risk factors, together with all of the other information included in this prospectus supplement and the accompanying prospectus, before you decide whether to make an investment in our securities. The risks set out below and in the accompanying prospectus are not the only risks we face. Additional risks and uncertainties not presently known to us or not presently deemed material by us may also impair our operations and performance. If any of the following events occur, our business, financial condition, results of operations and cash flows could be materially and adversely affected which could materially adversely affect our ability to repay principal and interest on the Notes. In addition, the market price of the Notes and our net asset value could decline, and you may lose all or part of your investment. The risk factors described below, together with those set forth in the accompanying prospectus, are the principal risk factors associated with an investment in our securities, including the Notes, as well as those factors generally associated with an investment company with investment objectives, investment policies, capital structure or trading markets similar to ours.

Risks Related to the Notes

The Notes will be unsecured and therefore will be effectively subordinated to any secured indebtedness we have currently incurred or may incur in the future.

The Notes will not be secured by any of our assets or any of the assets of our subsidiaries. As a result, the Notes are effectively subordinated to any secured indebtedness we or our subsidiaries have currently incurred and may incur in the future (or any indebtedness that is initially unsecured to which we subsequently grant security) to the extent of the value of the assets securing such indebtedness. In any liquidation, dissolution, bankruptcy or other similar proceeding, the holders of any of our existing or future secured indebtedness and the secured indebtedness of our subsidiaries may assert rights against the assets pledged to secure that indebtedness in order to receive full payment of their indebtedness before the assets may be used to pay other creditors, including the holders of the Notes. As of June 30, 2017, we had no outstanding borrowings under our Union Bank Facility, which is secured by debt investments in our portfolio companies and related assets, and no outstanding borrowings under our Wells Facility, which is secured by loans in the borrowing base for the Wells Facility.

The Notes will be structurally subordinated to the indebtedness and other liabilities of our subsidiaries.

The Notes are obligations exclusively of Hercules Capital, Inc. and not of any of our subsidiaries. None of our subsidiaries is a guarantor of the Notes and the Notes are not required to be guaranteed by any subsidiaries we may acquire or create in the future. A significant portion of the indebtedness required to be consolidated on our balance sheet is held through our SBIC subsidiaries. For example, at June 30, 2017, we have issued $190.2 million in SBA-guaranteed debentures in our SBIC subsidiaries. The assets of such subsidiaries are not directly available to satisfy the claims of our creditors, including holders of the Notes. See “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Financial Condition, Liquidity and Capital Resources” in the accompanying prospectus for more detail on the SBA-guaranteed debentures.

Except to the extent we are a creditor with recognized claims against our subsidiaries, all claims of creditors (including trade creditors), if any, of our subsidiaries will have priority over our equity interests in such subsidiaries (and therefore the claims of our creditors, including holders of the Notes) with respect to the assets of such subsidiaries. Even if we are recognized as a creditor of one or more of our subsidiaries, our claims would still be effectively subordinated to any security interests in the assets of any such subsidiary and to any indebtedness or other liabilities of any such subsidiary senior to our claims. Consequently, the Notes will be structurally subordinated to all indebtedness and other liabilities (including trade payables) of any of our subsidiaries and any subsidiaries that we may in the future acquire or establish as financing vehicles or otherwise.

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As of June 30, 2017, we had no outstanding borrowings under our Wells Facility, no outstanding borrowings under our Union Bank Facility and approximately $190.2 million of indebtedness outstanding incurred by our SBIC subsidiaries, HT II and HT III. All of such indebtedness would be structurally senior to the Notes. In addition, our subsidiaries may incur substantial additional indebtedness in the future, all of which would be structurally senior to the Notes.

The indenture under which the Notes will be issued will contain limited protection for holders of the Notes.

The indenture under which the Notes will be issued offers limited protection to holders of the Notes. The terms of the indenture and the Notes do not restrict our or any of our subsidiaries’ ability to engage in, or otherwise be a party to, a variety of corporate transactions, circumstances or events that could have an adverse impact on your investment in the Notes. In particular, the terms of the indenture and the Notes will not place any restrictions on our or our subsidiaries’ ability to:

Furthermore, the terms of the indenture and the Notes do not protect holders of the Notes in the event that we experience changes (including significant adverse changes) in our financial condition, results of operations or credit ratings, as they do not require that we or our subsidiaries adhere to any financial tests or ratios or specified levels of net worth, revenues, income, cash flow, or liquidity.

Our ability to recapitalize, incur additional debt and take a number of other actions that are not limited by the terms of the Notes may have important consequences for you as a holder of the Notes, including making it more difficult for us to satisfy our obligations with respect to the Notes or negatively affecting the trading value of the Notes.

Certain of our current debt instruments include more protections for their holders than the indenture and the Notes. See “Risk Factors—In addition to regulatory requirements that restrict our ability to raise capital, our

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Credit Facilities and the 2024 Notes contain various covenants which, if not complied with, could accelerate repayment under the facility or require us to repurchase the 2024 Notes thereby materially and adversely affecting our liquidity, financial condition, results of operations and ability to pay distributions” in the accompanying prospectus. In addition, other debt we issue or incur in the future could contain more protections for its holders than the indenture and the Notes, including additional covenants and events of default. The issuance or incurrence of any such debt with incremental protections could affect the market for, and trading levels and prices of, the Notes.

Our amount of debt outstanding may increase as a result of this offering. Our current indebtedness could adversely affect our business, financial condition and results of operations and our ability to meet our payment obligations under the Notes and our other debt.

The use of debt could have significant consequences on our future operations, including:

Any of the above-listed factors could have an adverse effect on our business, financial condition and results of operations and our ability to meet our payment obligations under the Notes and our other debt.

Our ability to meet our payment and other obligations under our financing arrangements depends on our ability to generate significant cash flow in the future. This, to some extent, is subject to general economic, financial, competitive, legislative and regulatory factors as well as other factors that are beyond our control. We cannot assure you that our business will generate cash flow from operations, or that future borrowings will be available to us under our financing arrangements or otherwise, in an amount sufficient to enable us to meet our payment obligations under the Notes and our other debt and to fund other liquidity needs. If we are not able to generate sufficient cash flow to service our debt obligations, we may need to refinance or restructure our debt, including the Notes, sell assets, reduce or delay capital investments, or seek to raise additional capital. If we are unable to implement one or more of these alternatives, we may not be able to meet our payment obligations under the Notes and our other debt.

We may not be able to repurchase the Notes upon a Change of Control Repurchase Event.

Upon the occurrence of a Change of Control Repurchase Event, as defined in the indenture, as supplemented, subject to certain conditions, we will be required to offer to repurchase all outstanding Notes at 100% of their principal amount, plus accrued and unpaid interest. The source of funds for that purchase of Notes will be our available cash or cash generated from our operations or other potential sources, including borrowings, investment repayments, sales of assets or sales of equity. We cannot assure you that sufficient funds from such sources will be available at the time of any Change of Control Repurchase Event to make required repurchases of Notes tendered. The terms of certain of our and our subsidiaries’ financing arrangements provide that certain change of control events will constitute an event of default thereunder entitling the lenders to accelerate any

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indebtedness outstanding under the our and our subsidiaries’ financing arrangements at that time and to terminate the financing arrangements. In addition, the indenture governing our 2022 Convertible Notes contains a provision that would require us to offer to purchase the 2022 Convertible Notes upon the occurrence of a fundamental change. A failure to purchase any tendered 2022 Convertible Notes would constitute an event of default under the indenture for the 2022 Convertible Notes, which would, in turn, constitute a default under the Credit Facilities and the indenture. Our and our subsidiaries’ future debt instruments may also contain similar restrictions and provisions. If the holders of the Notes exercise their right to require us to repurchase Notes upon a Change of Control Repurchase Event, the financial effect of this repurchase could cause a default under our and our subsidiaries’ future debt instruments, even if the Change of Control Repurchase Event itself would not cause a default. It is possible that we will not have sufficient funds at the time of the Change of Control Repurchase Event to make the required repurchase of the Notes and/or our other debt. See “Description of Notes—Offer to Repurchase Upon a Change of Control Repurchase Event.”

An active trading market for the Notes may not develop or be maintained, which could limit the market price of the Notes or your ability to sell them.

The Notes are a new issue of debt securities for which there currently is no trading market. We do not intend to apply for listing of the Notes on any securities exchange or for quotation of the Notes on any automated dealer quotation system. If no active trading market develops, you may not be able to resell your Notes at their fair market value or at all. If the Notes are traded after their initial issuance, they may trade at a discount from their initial offering price depending on prevailing interest rates, the market for similar securities, our credit ratings, general economic conditions, our financial condition, performance and prospects and other factors. The underwriters have advised us that they intend to make a market in the Notes, but they are not obligated to do so. The underwriters may discontinue any market-making in the Notes at any time at their sole discretion. Accordingly, we cannot assure you that a liquid trading market will develop or be maintained for the Notes, that you will be able to sell your Notes at a particular time or that the price you receive when you sell will be favorable. To the extent an active trading market does not develop or is not maintained, the liquidity and trading price for the Notes may be harmed. Accordingly, you may be required to bear the financial risk of an investment in the Notes for an indefinite period of time.

A downgrade, suspension or withdrawal of a credit rating assigned by a rating agency to us or our unsecured debt, if any, or change in the debt markets could cause the liquidity or market value of the Notes to decline significantly.

Our credit ratings are an assessment by rating agencies of our ability to pay our debts when due. Consequently, real or anticipated changes in our credit ratings will generally affect the market value of the Notes. These credit ratings may not reflect the potential impact of risks relating to the structure or marketing of the Notes. Credit ratings are not a recommendation to buy, sell or hold any security, and may be revised or withdrawn at any time by the issuing organization in its sole discretion. Neither we nor any underwriter undertakes any obligation to maintain our credit ratings or to advise holders of Notes of any changes in our credit ratings. There can be no assurance that our credit ratings will remain for any given period of time or that such credit ratings will not be lowered or withdrawn entirely by the rating agencies if in their judgment future circumstances relating to the basis of the credit ratings, such as adverse changes in our company, so warrant. The conditions of the financial markets and prevailing interest rates have fluctuated in the past and are likely to fluctuate in the future, which could have an adverse effect on the market prices of the Notes.

If we Default on our obligations to pay our other indebtedness, we may not be able to make payments on the Notes.

Any default under the agreements governing our indebtedness, including a default under the Wells Facility, the Union Bank Facility, the 2024 Notes, the 2022 Convertible Notes and the Asset-Backed Notes or other indebtedness to which we may be a party, that is not waived by the required lenders or holders, and the remedies

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sought by the holders of such indebtedness, could make us unable to pay principal, premium, if any, and interest on the Notes and substantially decrease the market value of the Notes. If we are unable to generate sufficient cash flow and are otherwise unable to obtain funds necessary to meet required payments of principal, premium, if any, and interest on our indebtedness, or if we otherwise fail to comply with the various covenants, including financial and operating covenants, in the instruments governing our indebtedness, we could be in default under the terms of the agreements governing such indebtedness. In the event of such default, the holders of such indebtedness could elect to declare all the funds borrowed thereunder to be due and payable, together with accrued and unpaid interest, the lenders under the Wells Facility and the Union Bank Facility or other debt we may incur in the future could elect to terminate their commitments, cease making further loans and institute foreclosure proceedings against our assets, and we could be forced into bankruptcy or liquidation. If our operating performance declines, we may in the future need to seek to obtain waivers from the required lenders under the Wells Facility or Union Bank Facility or the required holders of our 2024 Notes, 2022 Convertible Notes, Asset-Backed Notes or other debt that we may incur in the future to avoid being in default. If we breach our covenants under the Wells Facility, Union Bank Facility, the 2024 Notes, the 2022 Convertible Notes, the Asset-Backed Notes or other debt and seek a waiver, we may not be able to obtain a waiver from the required lenders or holders. If this occurs, we would be in default under the Wells Facility or Union Bank Facility, the 2024 Notes, the 2022 Convertible Notes, the Asset-Backed Notes or other debt, as applicable, the lenders or holders could exercise their rights as described above, and we could be forced into bankruptcy or liquidation. If we are unable to repay debt, lenders having secured obligations, including the lenders under the Wells Facility and the Union Bank Facility, could proceed against the collateral securing the debt. Because the Wells Facility and the Union Bank Facility have, and any future credit facilities will likely have, customary cross-default provisions, if the indebtedness under the Notes, the Wells Facility, Union Bank Facility, the 2024 Notes, the 2022 Convertible Notes or the Asset-Backed Notes or under any future credit facility is accelerated, we may be unable to repay or finance the amounts due. See “Specific Terms of the Notes and the Offering” in this prospectus supplement.

FATCA withholding may apply to payments to certain foreign entities.

Payments made under the Notes to a foreign financial institution or non-financial foreign entity (including such an institution or entity acting as an intermediary) may be subject to a U.S. withholding tax of 30% under U.S. Foreign Account Tax Compliance Act provisions of the Code (commonly referred to as “FATCA”). This U.S. withholding tax generally applies to payments of interest on the Notes as well as, after December 31, 2018, to any payments of gross proceeds (including principal payments) from the sale, redemption, retirement or other disposition of the Notes, unless the foreign financial institution or non-financial foreign entity complies with certain information reporting, withholding, identification, certification and related requirements imposed by FATCA. Depending upon the status of a holder and the status of an intermediary through which any Notes are held, the holder could be subject to this 30% U.S. withholding tax in respect of any interest paid on the Notes as well as any proceeds from the sale, redemption, retirement or other disposition of the Notes. Persons located in jurisdictions that have entered into an intergovernmental agreement with the United States to implement FATCA may be subject to different rules. You should consult your own tax advisors regarding FATCA and how it may affect your investment in the Notes. See “United States Federal Income Tax Matters—Taxation of Note Holders—FATCA” in this prospectus supplement for further information.

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USE OF PROCEEDS

We estimate that the net proceeds we will receive from the sale of the $             million aggregate principal amount of Notes in this offering will be approximately $            , based on a public offering of             % of par, after deducting the underwriting discount of approximately $             million payable by us and estimated offering expenses of approximately $             payable by us.

We expect to use the net proceeds from this offering (i) to repurchase or redeem all or a portion of our 2024 Notes, (ii) to fund investments in debt and equity securities in accordance with our investment objective, and (iii) for other general corporate purposes.

As of June 30, 2017, the aggregate principal balance of the 2024 Notes was approximately $258.5 million. The 2024 Notes bear interest at a rate of 6.25% per year, payable quarterly and mature, unless earlier repurchased or redeemed, on July 30, 2024.

We intend to seek to invest the net proceeds received in this offering as promptly as practicable after receipt thereof consistent with our investment objective. We anticipate that substantially all of the net proceeds from any offering of our securities will be used as described above within three to six months, depending on market conditions. We anticipate that the remainder will be used for working capital and general corporate purposes, including potential payments or distributions to shareholders. Pending such uses and investments, we will invest a portion of the net proceeds of this offering primarily in cash, cash equivalents, U.S. government securities or high-quality debt securities maturing in one year or less from the time of investment. Our ability to achieve our investment objectives may be limited to the extent that the net proceeds of this offering, pending full investment, are held in lower yielding short-term instruments.

The amount of net proceeds may be more or less than the amount described in this preliminary prospectus supplement depending on the amount of Notes we sell in the offering, which will be determined at pricing. To the extent that we receive more than the amount described in this preliminary prospectus supplement, we intend to use the net proceeds for investment in portfolio companies in accordance with our investment objective and strategies and for working capital and general corporate purposes. To the extent we receive less, the amount we have available for such purposes will be reduced.

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CAPITALIZATION

The following table sets forth (i) our actual capitalization as of June 30, 2017, and (ii) our capitalization as adjusted to give effect to the sale of $ aggregate principal amount of Notes in this offering, after deducting the underwriting discounts and commissions of approximately $ million payable by us and estimated offering expenses of approximately $ payable by us and the application of the net proceeds therefrom as described under “Use of Proceeds.” You should read this table together with the “Use of Proceeds” section and our statement of assets and liabilities included elsewhere in this prospectus supplement.

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RATIO OF EARNINGS TO FIXED CHARGES

The following contains our ratio of earnings to fixed charges for the periods indicated, computed as set forth below. You should read these ratios of earnings to fixed charges in connection with our consolidated financial statements, including the notes to those statements, included in this prospectus supplement:

For purposes of computing the ratios of earnings to fixed charges, earnings represent net increase in stockholders’ equity resulting from operations plus fixed charges. Fixed charges include interest and credit facility fees expense and amortization of debt issuance costs.

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DESCRIPTION OF NOTES

The following description of the particular terms of the       % Notes due 20     supplements and, to the extent inconsistent with, replaces the description of the general terms and provisions of the debt securities set forth in the accompanying prospectus.

We will issue the Notes under a base indenture dated as of March 6, 2012, between us and U.S. Bank National Association, as trustee (the “trustee”), as supplemented by a separate supplemental indenture to be dated as of the settlement date for the Notes. As used in this section, all references to the “indenture” mean the base indenture as supplemented by the supplemental indenture. The terms of the Notes include those expressly set forth in the indenture and those made part of the indenture by reference to the Trust Indenture Act of 1939, as amended, or the TIA.

The following description is a summary of the material provisions of the Notes and the indenture and does not purport to be complete. This summary is subject to and is qualified by reference to all the provisions of the Notes and the indenture, including the definitions of certain terms used in the indenture. We urge you to read these documents because they, and not this description, define your rights as a holder of the Notes.

For purposes of this description, references to “we,” “our” and “us” refer only to Hercules Capital, Inc. and not to any of its current or future subsidiaries and references to “subsidiaries” refer only to our consolidated subsidiaries and exclude any investments held by Hercules Capital in the ordinary course of business which are not, under GAAP, consolidated on the financial statements of Hercules Capital and its subsidiaries.

General

The Notes:

The indenture does not limit the amount of debt that may be issued by us or our subsidiaries under the indenture or otherwise. The indenture does not contain any financial covenants and does not restrict us from paying distributions or issuing or repurchasing our other securities. Other than restrictions described under “—Offer to Repurchase Upon a Change of Control Repurchase Event” and “—Merger, Consolidation or Sale of Assets” below, the indenture does not contain any covenants or other provisions designed to afford holders of the Notes protection in the event of a highly leveraged transaction involving us or in the event of a decline in our credit rating as the result of a takeover, recapitalization, highly leveraged transaction or similar restructuring involving us that could adversely affect such holders.

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We may, without the consent of the holders, issue additional Notes under the indenture with the same terms (except for the issue date, public offering price and, if applicable, the initial interest payment date) and with the same CUSIP numbers as the Notes offered hereby in an unlimited aggregate principal amount; provided that if such additional Notes are not fungible with the Notes offered hereby (or any other tranche of additional Notes) for U.S. federal income tax purposes, then such additional Notes will have different CUSIP numbers from the Notes offered hereby (and any such other tranche of additional Notes).

We do not intend to apply to list the Notes on any securities exchange or any automated dealer quotation system.

Payments on the Notes; Paying Agent and Registrar; Transfer and Exchange

We will pay the principal of, and interest on, Notes in global form registered in the name of or held by DTC or its nominee in immediately available funds to DTC or its nominee, as the case may be, as the registered holder of such Global Note (as defined below).

Payment of principal of (and premium, if any) and any such interest on the Notes will be made at the corporate trust office of the trustee in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that at our option payment of interest may be made by check mailed to the address of the person entitled thereto as such address shall appear in the security register.

A holder of Notes may transfer or exchange Notes at the office of the registrar in accordance with the indenture. The registrar and the trustee may require a holder, among other things, to furnish appropriate endorsements and transfer documents. No service charge will be imposed by us, the trustee or the registrar for any registration of transfer or exchange of Notes, but we may require a holder to pay a sum sufficient to cover any transfer tax or other similar governmental charge required by law or permitted by the indenture.

The registered holder of a Note will be treated as its owner for all purposes.

Interest

The Notes will bear cash interest at a rate of         % per year until maturity. Interest on the Notes will accrue from             , 2017 or from the most recent date on which interest has been paid or duly provided for. Interest will be payable semiannually in arrears on              and              of each year, beginning on             , 2018.

Interest will be paid to the person in whose name a Note is registered at 5:00 p.m. New York City time (the “close of business”) on              or             , as the case may be, immediately preceding the relevant interest payment date. Interest on the Notes will be computed on the basis of a 360-day year composed of twelve 30-day months.

If any interest payment date, redemption date, the maturity date or any earlier required repurchase date upon a Change of Control Repurchase Event (defined below) of a Note falls on a day that is not a business day, the required payment will be made on the next succeeding business day and no interest on such payment will accrue in respect of the delay. The term “business day” means, with respect to any Note, any day other than a Saturday, a Sunday or a day on which banking institutions in New York are authorized or obligated by law or executive order to close.

Ranking

The Notes will be our unsecured obligations that rank senior in right of payment to all of our existing and future indebtedness that is expressly subordinated, or junior, in right of payment to the Notes. The Notes will not be guaranteed by any of our current or future subsidiaries. The Notes will rank pari passu, or equally, in right of

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payment with all of our existing and future liabilities that are not so subordinated, or junior. The Notes will effectively rank subordinated, or junior, to any of our secured indebtedness (including unsecured indebtedness that we later secure) to the extent of the value of the assets securing such indebtedness. The Notes will rank structurally subordinated, or junior, to all existing and future indebtedness (including trade payables) incurred by our subsidiaries, financing vehicles or similar facilities. In the event of our bankruptcy, liquidation, reorganization or other winding up, our assets that secure secured debt will be available to pay obligations on the Notes only after all indebtedness under such secured debt has been repaid in full from such assets. We advise you that there may not be sufficient assets remaining to pay amounts due on any or all the Notes then outstanding.

As of June 30, 2017, our total consolidated indebtedness was approximately $766.4 million aggregate principal amount outstanding, of which approximately $87.7 million was secured indebtedness. After giving effect to the issuance of the Notes, our total consolidated indebtedness would have been approximately $             million aggregate principal amount outstanding as of June 30, 2017. See “Capitalization.”

Optional Redemption

We may redeem some or all of the Notes at any time, or from time to time. If we choose to redeem any Notes prior to maturity, we will pay a redemption price equal to the greater of the following amounts, plus, in each case, accrued and unpaid interest to the redemption date:

provided, however, that if we redeem any Notes on or after              (the date falling one month prior to the maturity date of the Notes), the redemption price for the Notes will be equal to 100% of the principal amount of the Notes to be redeemed, plus accrued and unpaid interest, if any, to, but excluding, the date of redemption.

If we choose to redeem any Notes, we will deliver a notice of redemption to holders of Notes not less than 30 nor more than 60 days before the redemption date. If we are redeeming less than all of the Notes, the particular Notes to be redeemed will be selected in accordance with the applicable procedures of the trustee and, so long as the Notes are registered to DTC or its nominee, DTC; provided, however, that no such partial redemption shall reduce the portion of the principal amount of a Note not redeemed to less than $2,000. Unless we default in payment of the redemption price, on and after the redemption date, interest will cease to accrue on the Notes or portions of the Notes called for redemption.

For purposes of calculating the redemption price in connection with the redemption of the Notes, on any redemption date, the following terms have the meanings set forth below:

“Treasury Rate” means, with respect to any redemption date, the rate per annum equal to the semi-annual equivalent yield-to-maturity of the Comparable Treasury Issue (computed as of the third business day immediately preceding the redemption), assuming a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for such redemption date. The redemption price and the Treasury Rate will be determined by us.

“Comparable Treasury Issue” means the United States Treasury security selected by the Reference Treasury Dealer as having a maturity comparable to the remaining term of the Notes to be redeemed that would be utilized, at the time of selection and in accordance with customary financing practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of the Notes being redeemed.

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“Comparable Treasury Price” means (1) the average of the remaining Reference Treasury Dealer Quotations for the redemption date, after excluding the highest and lowest Reference Treasury Dealer Quotations, or (2) if the Quotation Agent obtains fewer than four such Reference Treasury Dealer Quotations, the average of all such quotations.

“Quotation Agent” means a Reference Treasury Dealer selected by us.

“Reference Treasury Dealer” means each of (1) Citigroup Global Markets Inc. and (2) Jefferies LLC, or their respective affiliates which are primary U.S. government securities dealers and their respective successors; provided, however, that if any of the foregoing or their affiliates shall cease to be a primary U.S. government securities dealer in the United States (a “Primary Treasury Dealer”), we shall select another Primary Treasury Dealer.

“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any redemption date, the average, as determined by the Quotation Agent, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Quotation Agent by such Reference Treasury Dealer at 3:30 p.m. New York time on the third business day preceding such redemption date.

All determinations made by any Reference Treasury Dealer, including the Quotation Agent, with respect to determining the redemption price will be final and binding absent manifest error.

Offer to Repurchase Upon a Change of Control Repurchase Event

If a Change of Control Repurchase Event occurs, unless we have exercised our right to redeem the Notes in full, we will make an offer to each holder of Notes to repurchase all or any part (in minimum denominations of $2,000 and integral multiples of $1,000 principal amount) of that holder’s Notes at a repurchase price in cash equal to 100% of the aggregate principal amount of Notes repurchased plus any accrued and unpaid interest on the Notes repurchased to, but not including, the date of purchase. Within 30 days following any Change of Control Repurchase Event or, at our option, prior to any Change of Control, but after the public announcement of the Change of Control, we will mail a notice to each holder describing the transaction or transactions that constitute or may constitute the Change of Control Repurchase Event and offering to repurchase Notes on the payment date specified in the notice, which date will be no earlier than 30 days and no later than 60 days from the date such notice is mailed. The notice shall, if mailed prior to the date of consummation of the Change of Control, state that the offer to purchase is conditioned on the Change of Control Repurchase Event occurring on or prior to the payment date specified in the notice. We will comply with the requirements of Rule 14e-1 under the Exchange Act and any other securities laws and regulations thereunder to the extent those laws and regulations are applicable in connection with the repurchase of the Notes as a result of a Change of Control Repurchase Event. To the extent that the provisions of any securities laws or regulations conflict with the Change of Control Repurchase Event provisions of the Notes, we will comply with the applicable securities laws and regulations and will not be deemed to have breached our obligations under the Change of Control Repurchase Event provisions of the Notes by virtue of such conflict.

On the Change of Control Repurchase Event payment date, subject to extension if necessary to comply with the provisions of the 1940 Act, we will, to the extent lawful:

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The paying agent will promptly remit to each holder of Notes properly tendered the purchase price for the Notes, and the trustee will promptly authenticate and mail (or cause to be transferred by book-entry) to each holder a new Note equal in principal amount to any unpurchased portion of any Notes surrendered; provided that each new Note will be in a minimum principal amount of $2,000 or an integral multiple of $1,000 in excess thereof.

We will not be required to make an offer to repurchase the Notes upon a Change of Control Repurchase Event if a third party makes an offer in the manner, at the times and otherwise in compliance with the requirements for an offer made by us and such third party purchases all Notes properly tendered and not withdrawn under its offer.

The source of funds that will be required to repurchase Notes in the event of a Change of Control Repurchase Event will be our available cash or cash generated from our operations or other potential sources, including funds provided by a purchaser in the Change of Control transaction, borrowings, sales of assets or sales of equity. We cannot assure you that sufficient funds from such sources will be available at the time of any Change of Control Repurchase Event to make required repurchases of Notes tendered. The terms of certain of our and our subsidiaries’ financing arrangements provide that certain change of control events will constitute an event of default thereunder entitling the lenders to accelerate any indebtedness outstanding under the our and our subsidiaries’ financing arrangements at that time and to terminate the financing arrangements. In addition, the indenture governing our 2022 Convertible Notes contains a provision that would require us to offer to purchase the 2022 Convertible Notes upon the occurrence of a fundamental change. A failure to purchase any tendered 2022 Convertible Notes would constitute an event of default under the indenture for the 2022 Convertible Notes, which would, in turn, constitute a default under the Credit Facilities and the indenture. See “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Financial Condition, Liquidity and Capital Resources” in the accompanying prospectus for a general discussion of our indebtedness. Our and our subsidiaries’ future debt instruments may contain similar restrictions and provisions. If the holders of the Notes exercise their right to require us to repurchase Notes upon a Change of Control Repurchase Event, the financial effect of this repurchase could cause a default under our and our subsidiaries’ future debt instruments, even if the Change of Control Repurchase Event itself would not cause a default. It is possible that we will not have sufficient funds at the time of the Change of Control Repurchase Event to make the required repurchase of the Notes and/or our other debt. See “Risk Factors—Risks Relating to the Notes—We may not be able to repurchase the Notes upon a Change of Control Repurchase Event.”

The definition of “Change of Control” includes a phrase relating to the direct or indirect sale, transfer, conveyance or other disposition of “all or substantially all” of our properties or assets and those of our subsidiaries taken as a whole. Although there is a limited body of case law interpreting the phrase “substantially all,” there is no precise, established definition of the phrase under applicable law. Accordingly, the ability of a holder of Notes to require us to repurchase the Notes as a result of a sale, transfer, conveyance or other disposition of less than all of our assets and the assets of our subsidiaries taken as a whole to another person or group may be uncertain.

For purposes of the Notes:

“Below Investment Grade Rating Event” means the Notes are downgraded below Investment Grade by the Rating Agency on any date from the date of the public notice of an arrangement that results in a Change of Control until the end of the 60-day period following public notice of the occurrence of a Change of Control (which period shall be extended so long as the rating of the Notes is under publicly announced consideration for possible downgrade by the Rating Agency); provided that a Below Investment Grade Rating Event otherwise arising by virtue of a particular reduction in rating shall not be deemed to have occurred in respect of a particular Change of Control (and thus shall not be deemed a Below Investment Grade Rating Event for purposes of the definition of Change of Control Repurchase Event hereunder) if the Rating Agency making the reduction in rating to which this definition would otherwise apply does not announce or publicly confirm or inform the trustee

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in writing at its request that the reduction was the result, in whole or in part, of any event or circumstance comprised of or arising as a result of, or in respect of, the applicable Change of Control (whether or not the applicable Change of Control shall have occurred at the time of the Below Investment Grade Rating Event).

“Change of Control” means the occurrence of any of the following:

“Change of Control Repurchase Event” means the occurrence of a Change of Control and a Below Investment Grade Rating Event.

“Controlled Subsidiary” means any subsidiary of Hercules Capital, 50% or more of the outstanding equity interests of which are owned by Hercules Capital and its direct or indirect subsidiaries and of which Hercules Capital possesses, directly or indirectly, the power to direct or cause the direction of the management or policies, whether through the ownership of voting equity interests, by agreement or otherwise.

“Investment Grade” means a rating of BBB– or better by S&P (or its equivalent under any successor rating categories of S&P) or the equivalent of any other Rating Agency, as applicable, or in each case, the equivalent under any successor category of such Rating Agency.

“Kroll” means Kroll Bond Rating Agency, Inc., or any successor thereto.

“Permitted Holders” means (i) us and (ii) one or more of our Controlled Subsidiaries.

“Rating Agency” means:

“S&P” means Standard & Poor’s Ratings Services, a Standard & Poor’s Financial Services LLC business, or any successor thereto.

“Voting Stock” as applied to stock of any person, means shares, interests, participations or other equivalents in the equity interest (however designated) in such person having ordinary voting power for the election of a majority of the directors (or the equivalent) of such person, other than shares, interests, participations or other equivalents having such power only by reason of the occurrence of a contingency.

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Covenants

In addition to the covenants described in the base indenture, the following covenants shall apply to the Notes. To the extent of any conflict or inconsistency between the base indenture and the following covenants, the following covenants shall govern:

Merger, Consolidation or Sale of Assets

The indenture will provide that we will not merge or consolidate with or into any other person (other than a merger of a wholly owned subsidiary into us), or sell, transfer, lease, convey or otherwise dispose of all or substantially all our property (provided that, for the avoidance of doubt, a pledge of assets pursuant to any secured debt instrument of Hercules Capital or its Controlled Subsidiaries shall not be deemed to be any such sale, transfer, lease, conveyance or disposition) in any one transaction or series of related transactions unless:

For the purposes of this covenant, the sale, transfer, lease, conveyance or other disposition of all the property of one or more of our subsidiaries, which property, if held by us instead of such subsidiaries, would constitute all or substantially all of our property on a consolidated basis, shall be deemed to be the transfer of all or substantially all of our property.

Although there is a limited body of case law interpreting the phrase “substantially all,” there is no precise established definition of the phrase under applicable law. Accordingly, in certain circumstances there may be a degree of uncertainty as to whether a particular transaction would involve “all or substantially all” of the properties or assets of a person. As a result, it may be unclear as to whether the merger, consolidation or sale of assets covenant would apply to a particular transaction as described above absent a decision by a court of competent jurisdiction. Although these types of transactions are permitted under the indenture, certain of the foregoing transactions could constitute a Change of Control that results in a Change of Control Repurchase Event permitting each holder to require us to repurchase the Notes of such holder as described above.

An assumption by any person of obligations under the Notes and the indenture might be deemed for U.S. federal income tax purposes to be an exchange of the Notes for new Notes by the holders thereof, resulting in recognition of gain or loss for such purposes and possibly other adverse tax consequences to the holders. Holders should consult their own tax advisors regarding the tax consequences of such an assumption.

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Other Covenants

Events of Default

Each of the following is an event of default:

If an event of default occurs and is continuing, then and in every such case (other than an event of default specified in item (6) above) the trustee or the holders of at least 25% in principal amount of the outstanding Notes may declare the entire principal amount of Notes to be due and immediately payable, by a notice in writing to us (and to the trustee if given by the holders), and upon any such declaration such principal or specified portion thereof shall become immediately due and payable. Notwithstanding the foregoing, in the case of the events of bankruptcy, insolvency or reorganization described in item (6) above, 100% of the principal of and accrued and unpaid interest on the Notes will automatically become due and payable.

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At any time after a declaration of acceleration with respect to the Notes has been made and before a judgment or decree for payment of the money due has been obtained by the trustee, the holders of a majority in principal amount of the outstanding Notes, by written notice to us and the trustee, may rescind and annul such declaration and its consequences if (i) we have paid or deposited with the trustee a sum sufficient to pay all overdue installments of interest, if any, on all outstanding Notes, the principal of (and premium, if any, on) all outstanding Notes that have become due otherwise than by such declaration of acceleration and interest thereon at the rate or rates borne by or provided for in such Notes, to the extent that payment of such interest is lawful interest upon overdue installments of interest at the rate or rates borne by or provided for in such Notes, and all sums paid or advanced by the trustee and the reasonable compensation, expenses, disbursements and advances of the trustee, its agents and counsel, and (ii) all events of default with respect to the Notes, other than the nonpayment of the principal of (or premium, if any, on) or interest on such Notes that have become due solely by such declaration of acceleration, have been cured or waived. No such rescission will affect any subsequent default or impair any right consequent thereon.

No holder of Notes will have any right to institute any proceeding, judicial or otherwise, with respect to the indenture, or for the appointment of a receiver or trustee, or for any other remedy under the indenture, unless

Notwithstanding any other provision in the indenture, the holder of any Note shall have the right, which is absolute and unconditional, to receive payment of the principal of (and premium, if any, on) and interest, if any, on such Note on the stated maturity or maturity expressed in such Note (or, in the case of redemption, on the redemption date or, in the case of repayment at the option of the holders, on the repayment date) and to institute suit for the enforcement of any such payment, and such rights shall not be impaired without the consent of such holder.

The trustee shall be under no obligation to exercise any of the rights or powers vested in it by the indenture at the request or direction of any of the holders of the Notes unless such holders shall have offered to the trustee reasonable security or indemnity against the costs, expenses and liabilities which might be incurred by it in compliance with such request or direction. Subject to the foregoing, the holders of a majority in principal amount of the outstanding Notes shall have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee with respect to the Notes, provided that (i) such direction shall not be in conflict with any rule of law or with this indenture, (ii) the trustee may take any other action deemed proper by the trustee that is not inconsistent with such direction and (iii) the trustee need not take any action that it determines in good faith may involve it in personal liability or be unjustly prejudicial to the holders of Notes not consenting.

The holders of not less than a majority in principal amount of the outstanding Notes may on behalf of the holders of all of the Notes waive any past default under the indenture with respect to the Notes and its consequences, except a default (i) in the payment of (or premium, if any, on) or interest, if any, on any Note, or (ii) in respect of a covenant or provision of the indenture which cannot be modified or amended without the

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consent of the holder of each outstanding Note affected. Upon any such waiver, such default shall cease to exist, and any event of default arising therefrom shall be deemed to have been cured, for every purpose, but no such waiver shall extend to any subsequent or other default or event of default or impair any right consequent thereto.

We are required to deliver to the trustee, within 120 days after the end of each fiscal year, an officers’ certificate stating that to the knowledge of the signers whether we are in default in the performance of any of the terms, provisions or conditions of the indenture.

Within 90 days after the occurrence of any default under the indenture with respect to the Notes, the trustee shall transmit notice of such default known to the trustee, unless such default shall have been cured or waived; provided, however, that, except in the case of a default in the payment of the principal of (or premium, if any, on) or interest, if any, on any Note, the trustee shall be protected in withholding such notice if and so long as the Board of Directors, the executive committee or a trust committee of directors of the trustee in good faith determines that withholding of such notice is in the interest of the holders of the Notes.

Satisfaction and Discharge; Defeasance

We may satisfy and discharge our obligations under the indenture by delivering to the securities registrar for cancellation all outstanding Notes or by depositing with the trustee or delivering to the holders, as applicable, after the Notes have become due and payable, or otherwise, moneys sufficient to pay all of the outstanding Notes and paying all other sums payable under the indenture by us. Such discharge is subject to terms contained in the indenture.

In addition, the Notes are subject to defeasance and covenant defeasance, in each case, in accordance with the terms of the indenture. Defeasance means that, subject to the satisfaction of certain conditions, including, but not limited to, (i) depositing in trust for the benefit of the holders of the Notes a combination of money and/or U.S. government or U.S. government agency notes or bonds that will generate enough cash to make interest, principal and any other payments on the Notes on their various due date and (ii) delivering to the Trustee an opinion of counsel stating that (a) we have received from, or there has been published by, the Internal Revenue Service (the “IRS”) a ruling, or (b) since the date of execution of the indenture, there has been a change in the applicable federal income tax law, in either case to the effect that, and based thereon, the holders and beneficial owners of the Notes and any coupons appertaining thereto will not recognize income, gain or loss for federal income tax purposes as a result of such defeasance and will be subject to federal income tax on the same amounts, in the same manner and at the same times as would have been the case if such defeasance had not occurred, we can legally release ourselves from all payment and other obligations on the Notes. Covenant defeasance means that, subject to the satisfaction of certain conditions, including, but not limited to, (i) depositing in trust for the benefit of the holders of the Notes a combination of money and/or U.S. government or U.S. government agency notes or bonds that will generate enough cash to make interest, principal and any other payments on the Notes on their various due dates and (ii) delivering to the Trustee an opinion of counsel to the effect that the holders and beneficial owners of the Notes and any coupons appertaining thereto will not recognize income, gain or loss for federal income tax purposes as a result of such covenant defeasance and will be subject to federal income tax on the same amounts, in the same manner and at the same times as would have been the case if such covenant defeasance had not occurred, we will be released from some of the restrictive covenants in the indenture.

Trustee

U.S. Bank National Association is the trustee, security registrar and paying agent. U.S. Bank National Association, in each of its capacities, including without limitation as trustee, security registrar and paying agent, assumes no responsibility for the accuracy or completeness of the information concerning us or our affiliates or any other party contained in this document or the related documents or for any failure by us or any other party to

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disclose events that may have occurred and may affect the significance or accuracy of such information, or for any information provided to it by us, including but not limited to settlement amounts and any other information.

We may maintain banking relationships in the ordinary course of business with the trustee and its affiliates.

Governing Law

The indenture provides that it and the Notes shall be governed by and construed in accordance with the laws of the State of New York, without regard to principles of conflicts of laws that would cause the application of laws of another jurisdiction.

Book-Entry, Settlement and Clearance

Global Notes

The Notes will be initially issued in the form of one or more registered Notes in global form, without interest coupons (the “Global Notes”). Upon issuance, each of the Global Notes will be deposited with the trustee as custodian for DTC and registered in the name of Cede & Co., as nominee of DTC.

Ownership of beneficial interests in a Global Note will be limited to persons who have accounts with DTC (“DTC participants”) or persons who hold interests through DTC participants. We expect that under procedures established by DTC:

Beneficial interests in Global Notes may not be exchanged for Notes in physical, certificated form except in the limited circumstances described below.

Book-Entry Procedures for Global Notes

All interests in the Global Notes will be subject to the operations and procedures of DTC. We provide the following summary of those operations and procedures solely for the convenience of investors. The operations and procedures of DTC are controlled by that settlement system and may be changed at any time. Neither we nor the underwriters are responsible for those operations or procedures.

DTC has advised us that it is:

DTC was created to hold securities for its participants and to facilitate the clearance and settlement of securities transactions between its participants through electronic book-entry changes to the accounts of its participants. DTC’s participants include securities brokers and dealers, including the underwriters; banks and

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trust companies; clearing corporations and other organizations. Indirect access to DTC’s system is also available to others such as banks, brokers, dealers and trust companies; these indirect participants clear through or maintain a custodial relationship with a DTC participant, either directly or indirectly. Investors who are not DTC participants may beneficially own securities held by or on behalf of DTC only through DTC participants or indirect participants in DTC.

So long as DTC’s nominee is the registered owner of a Global Note, that nominee will be considered the sole owner or holder of the Notes represented by that Global Note for all purposes under the indenture. Except as provided below, owners of beneficial interests in a Global Note:

As a result, each investor who owns a beneficial interest in a Global Note must rely on the procedures of DTC to exercise any rights of a holder of Notes under the indenture (and, if the investor is not a participant or an indirect participant in DTC, on the procedures of the DTC participant through which the investor owns its interest).

Payments of principal and interest with respect to the Notes represented by a Global Note will be made by the trustee to DTC’s nominee as the registered holder of the Global Note. Neither we nor the Trustee will have any responsibility or liability for the payment of amounts to owners of beneficial interests in a Global Note, for any aspect of the records relating to or payments made on account of those interests by DTC, or for maintaining, supervising or reviewing any records of DTC relating to those interests.

Payments by participants and indirect participants in DTC to the owners of beneficial interests in a Global Note will be governed by standing instructions and customary industry practice and will be the responsibility of those participants or indirect participants and DTC.

Transfers between participants in DTC will be effected under DTC’s procedures and will be settled in same-day funds.

Certificated Notes

Notes in physical, certificated form will be issued and delivered to each person that DTC identifies as a beneficial owner of the related Notes only if:

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UNDERWRITING

We are offering the Notes described in this prospectus supplement and the accompanying prospectus through a number of underwriters. Citigroup Global Markets Inc. and Jefferies LLC are acting as representatives of the underwriters. We have entered into an underwriting agreement with the underwriters. Subject to the terms and conditions of the underwriting agreement, we have agreed to sell to the underwriters, and each underwriter has severally and not jointly agreed to purchase from us, the aggregate principal amount of Notes listed next to its name in the following table:

Subject to the terms and conditions set forth in the underwriting agreement, the underwriters have agreed, severally and not jointly, to purchase all of the Notes sold under the underwriting agreement if any of these Notes are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the nondefaulting underwriters may be increased or the underwriting agreement may be terminated.

We have agreed to indemnify the several underwriters against certain liabilities, including liabilities under the Securities Act, or to contribute to payments the underwriters may be required to make in respect of those liabilities.

The underwriters are offering the Notes, subject to prior sale, when, as and if issued to and accepted by them, subject to approval of legal matters by their counsel, and other conditions contained in the underwriting agreement, such as the receipt by the underwriters of officer’s certificates and legal opinions. The underwriters reserve the right to withdraw, cancel or modify offers to the public and to reject orders in whole or in part.

Commissions and Discounts

The following table shows the total underwriting discounts and commissions that we are to pay to the underwriters in connection with this offering.

The underwriters propose to offer some of the Notes to the public at the public offering price set forth on the cover page of this prospectus supplement and some of the Notes to certain other Financial Industry Regulatory Authority, Inc. (FINRA) members at the public offering price less a concession not in excess of         % of the aggregate principal amount of the Notes. The underwriters may allow, and the dealers may reallow, a discount not in excess of         % of the aggregate principal amount of the Notes. After the initial offering of the Notes to the public, the public offering price and such concessions may be changed. No such change shall change the amount of proceeds to be received by us as set forth on the cover page of this prospectus supplement.

No Sales of Similar Securities

We have agreed not to directly or indirectly sell, offer to sell, enter into any agreement to sell, or otherwise dispose of, any debt securities issued by the Company which are substantially similar to the Notes or securities

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convertible into such debt securities which are substantially similar to the Notes for a period of 30 days after the date of this prospectus supplement without first obtaining the written consent of the representatives. This consent may be given at any time without public notice.

Listing

The Notes are a new issue of securities with no established trading market. The Notes will not be listed on any securities exchange or quoted on any automated dealer quotation system.

We have been advised by certain of the underwriters that certain of the underwriters presently intend to make a market in the Notes after completion of this offering as permitted by applicable laws and regulations. Such underwriters are not obligated, however, to make a market in the Notes and any such market-making may be discontinued at any time in the sole discretion of such underwriters without any notice. Accordingly, no assurance can be given that an active and liquid public trading market for the Notes will develop or be maintained. If an active public trading market for the Notes does not develop, the market price and liquidity of the Notes may be adversely affected.

Price Stabilization, Short Positions

In connection with the offering, the underwriters may purchase and sell Notes in the open market. These transactions may include covering transactions and stabilizing transactions. Overallotment involves sales of securities in excess of the aggregate principal amount of securities to be purchased by the underwriters in the offering, which creates a short position for the underwriters. Covering transactions involve purchases of the securities in the open market after the distribution has been completed in order to cover short positions. Stabilizing transactions consist of certain bids or purchases of securities made for the purpose of preventing or retarding a decline in the market price of the securities while the offering is in progress.

The underwriters also may impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount received by it because the representatives have repurchased Notes sold by or for the account of such underwriter in stabilizing or short covering transactions.

Any of these activities may cause the price of the Notes to be higher than the price that otherwise would exist in the open market in the absence of such transactions. These transactions may be affected in the over-the-counter market or otherwise and, if commenced, may be discontinued at any time without any notice relating thereto.

Neither we nor any of the underwriters make any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of the Notes. In addition, neither we nor any of the underwriters make any representation that the representatives will engage in these transactions or that these transactions, once commenced, will not be discontinued without notice.

Electronic Offer, Sale and Distribution of Notes

The underwriters may make prospectuses available in electronic (PDF) format. A prospectus in electronic (PDF) format may be made available on a web site maintained by the underwriters, and the underwriters may distribute such prospectuses electronically. The underwriters may allocate a limited principal amount of the Notes for sale to their online brokerage customers.

Other Relationships

The underwriters and their affiliates have provided in the past and may provide from time to time in the future in the ordinary course of their business certain commercial banking, financial advisory, investment

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banking and other services to Hercules or our portfolio companies for which they have received or will be entitled to receive separate fees. In particular, the underwriters or their affiliates may execute transactions with Hercules or on behalf of Hercules or any of our portfolio companies.

The underwriters or their affiliates may also trade in our securities, securities of our portfolio companies or other financial instruments related thereto for their own accounts or for the account of others and may extend loans or financing directly or through derivative transactions to us or any of our portfolio companies.

We may purchase securities of third parties from the underwriters or their affiliates after the offering. However, we have not entered into any agreement or arrangement regarding the acquisition of any such securities, and we may not purchase any such securities. We would only purchase any such securities if—among other things—we identified securities that satisfied our investment needs and completed our due diligence review of such securities.

After the date of this prospectus supplement, the underwriters and their affiliates may from time to time obtain information regarding specific portfolio companies or us that may not be available to the general public. Any such information is obtained by the underwriters and their affiliates in the ordinary course of its business and not in connection with the offering of the Notes. In addition, after the offering period for the sale of the Notes, the underwriters or their affiliates may develop analyses or opinions related to Hercules or our portfolio companies and buy or sell interests in one or more of our portfolio companies on behalf of their proprietary or client accounts and may engage in competitive activities. There is no obligation on behalf of these parties to disclose their respective analyses, opinions or purchase and sale activities regarding any portfolio company or regarding us to our noteholders or any other persons.

In the ordinary course of their various business activities, the underwriters and their respective affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. Certain of the underwriters and their affiliates that have a lending relationship with us routinely hedge their credit exposure to us consistent with their customary risk management policies. Typically, such underwriters and their affiliates would hedge such exposure by entering into transactions which consist of either the purchase of credit default swaps or the creation of short positions in our securities, including potentially the Notes offered hereby. Any such short positions could adversely affect future trading prices of the Notes offered hereby. The underwriters and their affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

The principal business address of Citigroup Global Markets Inc. is 388 Greenwich Street, New York, New York 10013. The principal business address of Jefferies LLC is 520 Madison Avenue, New York, New York 10022.

European Economic Area

In relation to each Member State of the European Economic Area which has implemented the Prospectus Directive, each underwriter has represented and agreed that with effect from and including the date on which the Prospectus Directive is implemented in that Member State it has not made and will not make an offer of Notes to the public in that Member State, except that it may, with effect from and including such date, make an offer of Notes to the public in that Member State:

(a) to any legal entity that is a qualified investor as defined in the Prospectus Directive;

(b) to fewer than 100 or, if the Relevant Member State has implemented the relevant provisions of the 2010 PD Amending Directive, 150, natural or legal persons (other than qualified investors, as defined

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in the Prospectus Directive), as permitted under the Prospectus Directive, subject to obtaining the prior consent of the underwriters nominated by the Company for any such offer; or

(c) in any other circumstances falling within Article 3(2) of the Prospectus Directive, provided, that no such offer of Notes shall require the Company or any underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Directive or supplement a prospectus pursuant to Article 16 of the Prospectus Directive.

For the purposes of the above, the expression an “offer of Notes to the public” in relation to any Notes in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the Notes to be offered so as to enable an investor to decide to purchase or subscribe the Notes, as the same may be varied in that Member State by any measure implementing the Prospectus Directive in that Member State, and the expression “Prospectus Directive” means Directive 2003/71/EC (and amendments thereto, including the 2010 PD Amending Directive, to the extent implemented in the Relevant Member State), and includes any relevant implementing measure in the Relevant Member State and the expression “2010 PD Amending Directive” means Directive 2010/73/EU.

United Kingdom

Each underwriter has represented and agreed that:

(a) it has only communicated or caused to be communicated and will only communicate or cause to be communicated an invitation or inducement to engage in investment activity (within the meaning of Section 21 of the Financial Services and Markets Act of 2000 (the “FSMA”)) received by it in connection with the issue or sale of the Notes in circumstances in which Section 21(1) of the FSMA does not apply to the Company; and

(b) it has complied and will comply with all applicable provisions of the FSMA with respect to anything done by it in relation to the Notes in, from or otherwise involving the United Kingdom.

Other Jurisdictions

Other than in the United States, no action has been taken by us or the underwriters that would permit a public offering of the Notes offered by this prospectus supplement in any jurisdiction where action for that purpose is required. The Notes offered by this prospectus supplement may not be offered or sold, directly or indirectly, nor may this prospectus supplement or any other offering material or advertisements in connection with the offer and sale of any such Notes be distributed or published in any jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. Persons into whose possession this prospectus supplement comes are advised to inform themselves about and to observe any restriction relating to the offering and the distribution of this prospectus supplement. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell or a solicitation of an offer to buy the Notes offered by this prospectus supplement and the accompanying prospectus in any jurisdiction in which such an offer or a solicitation is unlawful.

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CERTAIN UNITED STATES FEDERAL INCOME TAX CONSIDERATIONS

The following discussion is a general summary of the material U.S. federal income tax considerations (and, in the case of a non-U.S. holder (as defined below), the material U.S. federal estate tax consequences) applicable to an investment in the Notes. This summary deals only with Notes that are purchased for cash in this offering for a price equal to the “issue price” of the Notes (i.e., the first price at which a substantial amount of the Notes is sold for money to investors, other than to bond houses, brokers or similar persons or organizations acting in the capacity of underwriters, placement agents or wholesalers). This summary does not purport to be a complete description of the income and estate tax considerations applicable to such an investment. The discussion is based upon the Code, Treasury Regulations, and administrative and judicial interpretations, each as of the date of this prospectus supplement and all of which are subject to change, potentially with retroactive effect. No assurance can be given that the IRS would not assert, or that a court would not sustain, a position contrary to any of the tax aspects set forth below. You should consult your own tax advisor with respect to tax considerations that pertain to your acquisition, ownership and disposition of our Notes. For a summary of the U.S. federal income tax considerations applicable to us regarding our election to be treated as a RIC, please refer to “Certain United States Federal Income Tax Considerations—Election to be Taxed as a RIC” and “Taxation as a Regulated Investment Company” in the accompanying prospectus.

This discussion deals only with Notes held as capital assets within the meaning of Section 1221 of the Code (generally, property held for investment purposes) and does not purport to deal with persons in special tax situations, such as financial institutions, insurance companies, regulated investment companies, dealers in securities or currencies, traders in securities, former citizens of the United States, persons holding the Notes as a hedge against currency risks or as a position in a “straddle,” “hedge,” “constructive sale transaction” or “conversion transaction” for tax purposes, entities that are tax-exempt for U.S. federal income tax purposes, retirement plans, individual retirement accounts, tax-deferred accounts, persons subject to the alternative minimum tax, pass-through entities (including partnerships and entities and arrangements classified as partnerships for U.S. federal income tax purposes) and beneficial owners of pass-through entities, or U.S. holders (as defined below) whose functional currency (as defined in Section 985 of the Code) is not the U.S. dollar. In addition, this discussion does not deal with any tax consequences other than U.S. federal income tax consequences (and, in the case of a non-U.S. holder, U.S. federal estate tax consequences). If you are considering acquiring the Notes, you should consult your own tax advisor concerning the application of the U.S. federal income and estate tax laws to you in light of your particular situation, as well as any consequences to you of purchasing, owning and disposing of the Notes under the laws of any other taxing jurisdiction.

For purposes of this discussion, the term “U.S. holder” means a beneficial owner of a Note that is, for U.S. federal income tax purposes, (i) an individual citizen or resident of the United States, (ii) a corporation or other entity treated as a corporation for U.S. federal income tax purposes, created or organized in or under the laws of the United States or of any state thereof or the District of Columbia, (iii) a trust (a) subject to the control of one or more U.S. persons and the primary supervision of a court in the United States, or (b) that existed on August 20, 1996 and has made a valid election (under applicable Treasury Regulations) to be treated as a domestic trust, or (iv) an estate the income of which is subject to U.S. federal income taxation regardless of its source.

The term “non-U.S. holder” means a beneficial owner of a Note that is neither a U.S. holder nor a partnership (including an entity or arrangement treated as a partnership for U.S. federal income tax purposes). An individual may, subject to certain exceptions, be subject to treatment as a resident alien, as opposed to a non-resident alien, for U.S. federal income tax purposes by, among other ways, being physically present in the U.S. (i) on at least 31 days during a calendar year, and (ii) for an aggregate period of at least 183 days during a three-year period ending in the current calendar year, counting for such purposes all of the days present in the current calendar year, one-third of the days present in the immediate preceding year, and one-sixth of the days present in the second preceding year. Resident aliens are subject to U.S. federal income tax as if they were U.S. citizens.

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If a partnership (including an entity or arrangement treated as a partnership for U.S. federal income tax purposes) holds any Notes, the U.S. federal income tax treatment of a partner of the partnership generally will depend upon the status of the partner, the activities of the partnership and certain determinations made at the partner level. Partnerships holding Notes, and the persons holding interests in such partnerships, should consult their own tax advisors as to the consequences of investing in the Notes in their individual circumstances.

Taxation of Note Holders

Taxation of U.S. Holders.

Except as discussed below, payments or accruals of interest on a Note generally will be taxable to a U.S. holder as ordinary interest income at the time they are received (actually or constructively) or accrued, in accordance with the U.S. holder’s regular method of tax accounting.

Upon the sale, exchange, redemption, retirement or other taxable disposition of a Note, a U.S. holder generally will recognize capital gain or loss equal to the difference between the amount realized on the sale, exchange, redemption, retirement or other taxable disposition (excluding amounts representing accrued and unpaid interest, which are treated as ordinary income to the extent not previously included in income) and the U.S. holder’s adjusted tax basis in the Note. A U.S. holder’s adjusted tax basis in a Note generally will equal the U.S. holder’s initial investment in the Note. Capital gain or loss generally will be long-term capital gain or loss if the U.S. holder’s holding period in the Note was more than one year. Long-term capital gains generally are taxed at reduced rates for individuals and certain other non-corporate U.S. holders. The distinction between capital gain and loss and ordinary income and loss also is important for purposes of, among other things, the limitations imposed on a U.S. holder’s ability to offset capital losses against ordinary income.

A tax of 3.8% will be imposed on certain “net investment income” (or “undistributed net investment income,” in the case of estates and trusts) received by U.S. holders with modified adjusted gross income above certain threshold amounts. “Net investment income” as defined for U.S. federal Medicare contribution purposes generally includes interest payments on and gain recognized from the sale, redemption, retirement or other disposition of the Notes. U.S. holders should consult their own tax advisors regarding the effect, if any, of this tax on their ownership and disposition of the Notes.

Under applicable Treasury Regulations, if a U.S. holder recognizes a loss with respect to the Notes or shares of our common stock of $2 million or more for a non-corporate U.S. holder or $10 million or more for a corporate U.S. holder in any single taxable year (or a greater loss over a combination of taxable years), the U.S. holder may be required to file with the IRS a disclosure statement on IRS Form 8886. Direct U.S. holders of portfolio securities are in many cases excepted from this reporting requirement, but, under current guidance, U.S. holders of a RIC are not excepted. Future guidance may extend the current exception from this reporting requirement to U.S. holders of most or all RICs. The fact that a loss is reportable under these regulations does not affect the legal determination of whether the taxpayer’s treatment of the loss is proper. Significant monetary penalties apply to a failure to comply with this reporting requirement. States may also have a similar reporting requirement. U.S. holders of the Notes or our common stock should consult their own tax advisors to determine the applicability of these Treasury Regulations in light of their individual circumstances.

Taxation of Non-U.S. Holders. Except as provided below under “Information Reporting and Backup Withholding” and “FATCA,” a non-U.S. holder generally will not be subject to U.S. federal income or withholding taxes on payments of principal or interest on a Note provided that (i) income on the Note is not effectively connected with the conduct by the non-U.S. holder of a trade or business within the United States, (ii) the non-U.S. holder is not a controlled foreign corporation related to the Company through stock ownership, (iii) the non-U.S. holder is not a bank receiving interest described in Section 881(c)(3)(A) of the Code, (iv) the non-U.S. holder does not own (directly or indirectly, actually or constructively) 10% or more of the total combined voting power of all classes of stock of the Company, and (v)(A) the non-U.S. holder provides the

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applicable withholding agent with a valid certification on an IRS Form W-8BEN, Form W-8BEN-E, or other applicable U.S. nonresident withholding tax certification form, certifying its non-U.S. holder status, or (B) a securities clearing organization, bank, or other financial institution that holds customer securities in the ordinary course of its trade or business (i.e., a “financial institution”) and holds a Note on a non-U.S. holder’s behalf certifies to the applicable withhold agent under penalties of perjury that either it or another financial institution has received the required statement from the non-U.S. holder certifying that it is a non-U.S. person and furnishes the applicable withhold agent with a copy of the statement.

A non-U.S. holder that is not exempt from tax under these rules generally will be subject to U.S. federal income tax withholding on payments of interest on the Notes at a rate of 30% unless (i) the income is effectively connected with the conduct of a U.S. trade or business, so long as the non-U.S. holder has provided the applicable withhold agent with an IRS Form W-8ECI or substantially similar substitute U.S. nonresident withholding tax certification form stating that the interest on the Notes is effectively connected with the non-U.S. holder’s conduct of a trade or business in the U.S. in which case the interest will be subject to U.S. federal income tax on a net income basis as applicable to U.S. holders generally (unless an applicable income tax treaty provides otherwise), or (ii) an applicable income tax treaty or provision in the Code provides for a lower rate of, or exemption from, withholding tax, so long as the non-U.S. holder has provided the applicable withhold agent with an IRS Form W-8BEN or Form W-8BEN-E (or other applicable U.S. nonresident withholding tax certification form) signed under penalties of perjury, claiming such lower rate of, or exemption from, withholding tax under such income tax treaty.

To claim the benefit of an income tax treaty or to claim exemption from withholding because income is effectively connected with a U.S. trade or business, the non-U.S. holder must timely provide the appropriate, properly executed IRS U.S. nonresident withholding tax certification form, signed under penalties of perjury, to the applicable withholding agent. These forms may be required to be updated periodically. Additionally, a non-U.S. holder who is claiming the benefits of an income tax treaty may be required to obtain a U.S. taxpayer identification number and provide certain documentary evidence issued by a non-U.S. governmental authority in order to prove residence in a foreign country.

In the case of a non-U.S. holder that is a corporation and that receives income that is effectively connected with the conduct of a U.S. trade or business, such income may also be subject to a branch profits tax (which is generally imposed on a non-U.S. corporation on the actual or deemed repatriation from the United States of earnings and profits attributable to a U.S. trade or business) at a 30% rate. The branch profits tax may not apply (or may apply at a reduced rate) if the non-U.S. holder is a qualified resident of a country with which the United States has an income tax treaty and provides the applicable withhold agent with an IRS Form W-8BEN or Form W-8BEN-E claiming exemption from, or entitlement to a lower rate of, branch profits tax under such treaty.

Generally, a non-U.S. holder will not be subject to U.S. federal income or withholding taxes on any amount that constitutes capital gain upon the sale, exchange, redemption, retirement or other taxable disposition of a Note, provided that the gain is not effectively connected with the conduct of a trade or business in the United States by the non-U.S. holder (and, if required by an applicable income tax treaty, is not attributable to a United States “permanent establishment” maintained by the non-U.S. holder). Non-U.S. holders should consult their own tax advisors with regard to whether taxes will be imposed on capital gain in their individual circumstances.

A Note that is held by an individual who, at the time of death, is not a citizen or resident of the United States (as specially defined for U.S. federal estate tax purposes) generally will not be subject to the U.S. federal estate tax, unless, at the time of death, (i) such individual directly or indirectly, actually or constructively, owns ten percent or more of the total combined voting power of all classes of our stock entitled to vote within the meaning of Section 871(h)(3) of the Code and the Treasury Regulations thereunder or (ii) such individual’s interest in the Notes is effectively connected with the individual’s conduct of a U.S. trade or business.

Information Reporting and Backup Withholding. A U.S. holder (other than an “exempt recipient,” including a corporation and certain other persons who, when required, demonstrate their exempt status) may be

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subject to backup withholding at a rate of 28% on, and to information reporting requirements with respect to, payments of principal and interest on, and proceeds from the sale, exchange, redemption or retirement of, the Notes. In general, if a non-corporate U.S. holder subject to information reporting fails to furnish a correct taxpayer identification number or otherwise fails to comply with applicable backup withholding requirements, backup withholding at the applicable rate may apply.

If you are a non-U.S. holder, generally, the applicable withholding agent must report to the IRS and to you payments of interest on the Notes and the amount of tax, if any, withheld with respect to those payments. Copies of the information returns reporting such interest payments and any withholding may also be made available to the tax authorities in the country in which you reside under the provisions of a treaty or agreement. In general, backup withholding will not apply to payments of interest on your Notes if you have provided to the applicable withholding agent the required certification that you are not a U.S. person and the applicable withholding agent does not have actual knowledge or reason to know that you are a U.S. person. Information reporting and, depending on the circumstances, backup withholding will apply to payment to you of the proceeds of a sale or other disposition (including a retirement or redemption) of the Notes within the U.S. or conducted through certain U.S.-related financial intermediaries, unless you certify under penalties of perjury that you are not a U.S. person or you otherwise establish an exemption, and the applicable withholding agent does not have actual knowledge or reason to know that you are a U.S. person.

In addition, backup withholding tax and certain other information reporting requirements apply to payments of principal and interest on, and proceeds from the sale, exchange, redemption or retirement of, the Notes held by a non-U.S. holder, unless an exemption applies. Backup withholding and information reporting will not apply to payments we make to a non-U.S. holder if such non-U.S. holder has provided to the applicable withholding agent under penalties of perjury the required certification of their non-U.S. person status as discussed above (and the applicable withholding agent does not have actual knowledge or reason to know that they are a U.S. person) or if the non-U.S. holder is an exempt recipient.

If a non-U.S. holder sells or redeems a Note through a U.S. broker or the U.S. office of a foreign broker, the proceeds from such sale or redemption will be subject to information reporting and backup withholding unless such non-U.S. holder provides the applicable withhold agent with a withholding certificate or other appropriate documentary evidence establishing that such non-U.S. holder is not a U.S. person to the broker and such broker does not have actual knowledge or reason to know that such non-U.S. holder is a U.S. person, or the non-U.S. holder is an exempt recipient eligible for an exemption from information reporting and backup withholding. If a non-U.S. holder sells or redeems a Note through the foreign office of a broker who is a U.S. person or has certain enumerated connections with the United States, the proceeds from such sale or redemption will be subject to information reporting unless the non-U.S. holder provides to such broker a withholding certificate or other appropriate documentary evidence establishing that the non-U.S. holder is not a U.S. person and such broker does not have actual knowledge or reason to know that such evidence is false, or the non-U.S. holder is an exempt recipient eligible for an exemption from information reporting. In circumstances where information reporting by the foreign office of such a broker is required, backup withholding will be required only if the broker has actual knowledge that the non-U.S. holder is a U.S. person.

You should consult your tax advisor regarding the qualification for an exemption from backup withholding and information reporting and the procedures for obtaining such an exemption, if applicable. Any amounts withheld under the backup withholding rules from a payment to a beneficial owner generally would be allowed as a refund or a credit against such beneficial owner’s U.S. federal income tax provided the required information is timely furnished to the IRS.

FATCA. Certain provisions of the Code, known as FATCA, generally impose a withholding tax of 30% on certain payments to certain foreign entities (including financial intermediaries) unless various U.S. information reporting and diligence requirements (that are in addition to the requirement to deliver an applicable U.S. nonresident withholding tax certification form (e.g., IRS Form W-8BEN), as discussed above) and certain other

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requirements have been satisfied. FATCA withholding generally applies to payments of interest and, after December 31, 2018, payments of gross proceeds (including principal payments) from the sale, redemption, retirement or other disposition of debt securities that can produce U.S. source interest (such as the Notes) (collectively, “withholdable payments”) to certain non-U.S. entities (including, in some circumstances, where such an entity is acting as an intermediary) that fail to comply with certain certification, identification, withholding and information reporting requirements imposed by FATCA. FATCA withholding taxes generally apply to all withholdable payments without regard to whether the beneficial owner of the payment would otherwise be entitled to an exemption from withholding taxes pursuant to an applicable income tax treaty with the U.S. or under U.S. domestic law. If FATCA withholding taxes are imposed with respect to any payments of interest or proceeds made under the Notes, holders that are otherwise eligible for an exemption from, or reduction of, U.S. federal withholding taxes with respect to such interest or proceeds will be required to seek a credit or refund from the IRS in order to obtain the benefit of such exemption or reduction, if any. Holders of or prospective holders of the Notes may be required to provide additional information to enable the applicable withholding agent to determine whether withholding is required. Persons located in jurisdictions that have entered into an intergovernmental agreement with the U.S. to implement FATCA may be subject to different rules. Non-U.S. holders, and U.S. holders that expect to hold the Notes through non-U.S. entities, should consult their own tax advisors regarding the effect, if any, of these withholding and reporting provisions.

The preceding discussion of material U.S. federal income tax considerations is for general information only and is not tax advice. We urge you to consult your own tax advisor with respect to the particular tax consequences to you of an investment in the Notes, including the possible effect of any pending legislation or proposed regulations.

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LEGAL MATTERS

Certain legal matters in connection with the securities offered hereby will be passed upon for us by Dechert LLP, Philadelphia, PA. Certain legal matters in connection with the securities offered hereby will be passed upon for the underwriters by Fried, Frank, Harris, Shriver & Jacobson LLP, New York, NY.

EXPERTS

The consolidated financial statements as of December 31, 2016 and 2015 and for each of the three years in the period ended December 31, 2016 and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) as of December 31, 2016 included in the accompanying prospectus have been so included in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

AVAILABLE INFORMATION

We have filed with the SEC a registration statement on Form N-2, together with all amendments and related exhibits, under the Securities Act, with respect to our securities offered by this prospectus supplement and the accompanying prospectus. The registration statement contains additional information about us and our securities being offered by this prospectus supplement and the accompanying prospectus.

We file annual, quarterly and current periodic reports, proxy statements and other information with the SEC under the Exchange Act. You may inspect and copy these reports, proxy statements and other information, as well as the registration statement of which this prospectus supplement and accompanying prospectus form a part and the related exhibits and schedules, at the Public Reference Room of the SEC at 100 F Street, N.E., Washington, D.C. 20549-0102. You may obtain information on the operation of the Public Reference Room by calling the SEC at 202-551-8090. The SEC maintains an Internet website that contains reports, proxy and information statements and other information filed electronically by us with the SEC which are available on the SEC’s Internet website at http://www.sec.gov. Copies of these reports, proxy and information statements and other information may be obtained, after paying a duplicating fee, by electronic request at the following E-mail address: publicinfo@sec.gov, or by writing the SEC’s Public Reference Section, Washington, D.C. 20549-0102.

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$600,000,000

Common Stock

Preferred Stock

Warrants

Subscription Rights

Debt Securities

This prospectus relates to the offer, from time to time, in one or more offerings or series, up to $600,000,000 of shares of our common stock, par value $0.001 per share, preferred stock, par value $0.001 per share, warrants representing rights to purchase shares of our common stock, preferred stock or debt securities, subscription rights or debt securities, which we refer to, collectively, as the “securities.” The preferred stock, debt securities, subscription rights and warrants offered hereby may be convertible or exchangeable into shares of our common stock. We may sell our securities through underwriters or dealers, “at-the-market” to or through a market maker into an existing trading market or otherwise directly to one or more purchasers, including existing stockholders in a rights offering, or through agents or through a combination of methods of sale, including auctions. The identities of such underwriters, dealers, market makers or agents, as the case may be, will be described in one or more supplements to this prospectus. The securities may be offered at prices and on terms to be described in one or more supplements to this prospectus.

In the event we offer common stock, the offering price per share will not be less than the net asset value per share of our common stock at the time we make the offering except (1) in connection with a rights offering to our existing stockholders, (2) with the consent of the holders of the majority of our voting securities and approval of our Board of Directors, or (3) under such circumstances as the Securities and Exchange Commission may permit. See “Risk Factors” for more information.

We are a specialty finance company focused on providing senior secured loans to high-growth, innovative venture capital-backed companies in a variety of technology, life sciences and sustainable and renewable technology industries. We primarily finance privately-held companies backed by leading venture capital and private equity firms and publicly-traded companies that lack access to public capital or are sensitive to equity ownership dilution. We source our investments through our principal office located in Palo Alto, CA, as well as through additional offices in Boston, MA, New York, NY, Washington, DC, Santa Monica, CA, Hartford, CT and San Diego, CA. Our goal is to be the leading structured debt financing provider for venture capital-backed companies in technology-related industries requiring sophisticated and customized financing solutions. We invest primarily in structured debt with warrants and, to a lesser extent, in senior debt and equity investments. We use the term “structured debt with warrants” to refer to any debt investment, such as a senior or subordinated secured loan, that is coupled with an equity component, including warrants, options or other rights to purchase common or preferred stock. Our structured debt with warrants investments typically are secured by some or all of the assets of the portfolio company. We invest primarily in private companies but also have investments in public companies.

Our investment objective is to maximize our portfolio total return by generating current income from our debt investments and capital appreciation from our warrant and equity-related investments. We are an internally-managed, non-diversified closed-end investment company that has elected to be regulated as a business development company under the Investment Company Act of 1940, as amended.

Our common stock is traded on the New York Stock Exchange, or NYSE, under the symbol “HTGC.” On August 30, 2017, the last reported sale price of a share of our common stock on the NYSE, was $12.31. The net asset value per share of our common stock at June 30, 2017 (the last date prior to the date of this prospectus on which we determined net asset value) was $9.87.

An investment in our securities may be speculative and involves risks including a heightened risk of total loss of investment. In addition, the companies in which we invest are subject to special risks. See “Risk Factors” beginning on page 14 to read about risks that you should consider before investing in our securities, including the risk of leverage.

Please read this prospectus before investing and keep it for future reference. It contains important information about us that a prospective investor ought to know before investing in our securities. We file annual, quarterly and current reports, proxy statements and other information about us with the Securities and Exchange Commission. The information is available free of charge by contacting us at 400 Hamilton Avenue, Suite 310, Palo Alto, California 94301 or by telephone calling collect at (650) 289-3060 or on our website at www.htgc.com. The SEC also maintains a website at www.sec.gov that contains such information.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

This prospectus may not be used to consummate sales of any securities unless accompanied by a prospectus supplement.

The date of this prospectus is September 7, 2017

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You should rely only on the information contained in this prospectus. We have not authorized any dealer, salesperson or other person to provide you with different information or to make representations as to matters not stated in this prospectus. If anyone provides you with different or inconsistent information, you should not rely on it. This prospectus is not an offer to sell, or a solicitation of an offer to buy, any securities by any person in any jurisdiction where it is unlawful for that person to make such an offer or solicitation or to any person in any jurisdiction to whom it is unlawful to make such an offer or solicitation. The information in this prospectus is accurate only as of its date, and under no circumstances should the delivery of this prospectus or the sale of any securities imply that the information in this prospectus is accurate as of any later date or that the affairs of Hercules Capital, Inc. have not changed since the date hereof. This prospectus will be updated to reflect material changes.

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Hercules Capital, Inc., our logo and other trademarks of Hercules Capital, Inc. mentioned in this prospectus are the property of Hercules Capital, Inc. All other trademarks or trade names referred to in this prospectus are the property of their respective owners.

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we have filed with the Securities and Exchange Commission using the “shelf” registration process. Under the shelf registration process, which constitutes a delayed offering in reliance on Rule 415 under the Securities Act of 1933, as amended (the “Securities Act”), we may offer, from time to time, up to $600,000,000 of our common stock, preferred stock, warrants representing rights to purchase shares of our common stock, preferred stock or debt securities, subscription rights or debt securities on the terms to be determined at the time of the offering. We may sell our securities through underwriters or dealers, “at-the-market” to or through a market maker, into an existing trading market or otherwise directly to one or more purchasers, including existing stockholders in a rights offering, or through agents or through a combination of methods of sale. The identities of such underwriters, dealers, market makers or agents, as the case may be, will be described in one or more supplements to this prospectus. The securities may be offered at prices and on terms described in one or more supplements to this prospectus. This prospectus provides you with a general description of the securities that we may offer. Each time we use this prospectus to offer securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. Please carefully read this prospectus and any such supplements together with the additional information described under “Where You Can Find Additional Information” in the “Summary” and “Risk Factors” sections before you make an investment decision.

A prospectus supplement may also add to, update or change information contained in this prospectus.

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1

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2

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FEES AND EXPENSES

The following table is intended to assist you in understanding the various costs and expenses that an investor in our common stock will bear directly or indirectly. However, we caution you that some of the percentages indicated in the table below are estimates and may vary. The footnotes to the fee table state which items are estimates. Except where the context suggests otherwise, whenever this prospectus contains a reference to fees or expenses paid by “you” or “us” or that “we” will pay fees or expenses, stockholders will indirectly bear such fees or expenses as investors in Hercules Capital, Inc.

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Example

The following example demonstrates the projected dollar amount of total cumulative expenses that would be incurred over various periods with respect to a hypothetical investment in our common stock. These amounts are based upon our payment of annual operating expenses at the levels set forth in the table above and assume no additional leverage.

The example and the expenses in the tables above should not be considered a representation of our future expenses, and actual expenses may be greater or lesser than those shown. Moreover, while the example assumes, as required by the applicable rules of the SEC, a 5% annual return, our performance will vary and may result in a return greater or lesser than 5%. In addition, while the example assumes reinvestment of all distributions at net asset value (“NAV”), participants in our dividend reinvestment plan may receive shares valued at the market price in effect at that time. This price may be at, above or below NAV. See “Dividend Reinvestment Plan” for additional information regarding our dividend reinvestment plan.

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Index to Financial Statements

SELECTED CONSOLIDATED FINANCIAL DATA

The selected consolidated financial data should be read in conjunction with “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” “Senior Securities” and the consolidated financial statements and related notes included elsewhere herein. The selected balance sheet data as of the end of fiscal year 2016, 2015, 2014, 2013, and 2012 and the financial statement of operations data for fiscal 2016, 2015, 2014, 2013, and 2012 has been derived from our audited financial statements, which have been audited by PricewaterhouseCoopers LLP, our independent registered public accounting firm, but not all of which are presented in this Form N-2.” The historical data are not necessarily indicative of results to be expected for any future period. The selected financial and other data for the six months ended June 30, 2017 and other quarterly financial information is derived from our unaudited financial statements, but in the opinion of management, reflects all adjustments (consisting only of normal recurring adjustments) that are necessary to present fairly the results of such interim periods. Interim results as of and for the six months ended June 30, 2017 are not necessarily indicative of the results that may be expected for the year ending December 31, 2017.

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Index to Financial Statements