Table of Contents

FORM OF PROSPECTUS SUPPLEMENT FOR DEBT OFFERINGS

Exhibit (s)(3)

The information in this preliminary prospectus supplement is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus supplement is not an offer to sell these securities and is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

[FORM OF PROSPECTUS SUPPLEMENT TO BE USED IN

CONJUNCTION WITH FUTURE DEBT SECURITIES OFFERINGS]

PROSPECTUS SUPPLEMENT

(to Prospectus dated             , 2012)

$

HERCULES

TECHNOLOGY GROWTH CAPITAL, INC.

% Senior [Subordinated] [Secured] Notes due

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

We are offering $             in aggregate principal amount of             % senior [subordinated] [secured] notes due             , or the “Notes.” The Notes will mature on             ,             . We will pay interest on the Notes             on             ,             ,             and             of each year, beginning on             ,             . We may redeem the Notes in whole or in part at any time or from time to time on or after             , at the redemption prices set forth under “Specific Terms of the Notes and the Offering—Optional             Redemption” in this prospectus supplement. The Notes will be issued in minimum denominations of $             and integral multiples of $             in excess thereof.

The Notes will be our direct senior [subordinated] [secured/unsecured] obligations and rank pari passu with all outstanding and future [secured/unsecured] [unsubordinated/subordinated] indebtedness.

[We intend to list the Notes on             , and we expect trading in the Notes on             to begin within         days of the original issue date. The Notes are expected to trade “flat,” which means that purchasers will not pay, and sellers will not receive, any accrued and unpaid interest on the Notes that is not reflected in the trading price. Currently, there is no public market for the Notes.]

An investment in our common stock involves risks, including the risk of a total loss of investment. In addition, the companies in which we invest are subject to special risks. See “Risk Factors” beginning on page [ ] of the accompanying prospectus and page S-[ ] in this prospectus supplement to read about risks you should consider before investing in our securities, including the risk of leverage.

This prospectus contains important information you should know before investing in the Notes. Please read this 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. 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.herculestech.com. The information on our website is not incorporated by reference into this prospectus or the accompanying prospectus. 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.

[In addition, the underwriters may purchase up to an additional $             aggregate principal amount of the Notes at the public offering price, less the sales load payable by us, to cover over-allotments, if any, within days from the date of this prospectus supplement. If the underwriters exercise this option in full, the total sales load paid by us will be $            , and total proceeds, before expenses, will be $            .

The underwriters are offering the Notes as set forth in “Underwriting.” Delivery of the Notes in book-entry form through The Depository Trust Company will be made on or about             , 2012.

The date of this prospectus supplement is             , 2012

[Underwriters]

            , 2012

Table of Contents

ABOUT THIS PROSPECTUS SUPPLEMENT

You should rely only on the information contained in this prospectus supplement and the accompanying prospectus. Neither we nor the underwriters have authorized any other person to provide you with different information from that contained in this prospectus supplement or the accompanying prospectus. If anyone provides you with different or inconsistent information, you should not rely on it. This prospectus supplement and the accompanying prospectus do not constitute an offer to sell, or a solicitation of an offer to buy, our 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 contained in this prospectus supplement and the accompanying prospectus is complete and accurate only as of their respective dates, regardless of the time of their delivery or sale of our securities. This prospectus supplement supersedes the accompanying prospectus to the extent it contains information different from or additional to the information in that prospectus.

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.

Table of Contents

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT

PROSPECTUS

Table of Contents

PROSPECTUS SUPPLEMENT SUMMARY

Our Company

We are a specialty finance company that provides debt and equity growth capital to technology-related companies at various stages of development from seed and emerging growth to expansion and established stages of development, which include select publicly listed companies and select lower middle market companies. Our investment objective is to maximize our portfolio total return by generating current income from our debt investments and capital appreciation from our equity-related investments. We are an internally-managed, non-diversified closed-end investment company that has elected to be treated as a business development company under the Investment Company Act of 1940, or the 1940 Act.

As of [    ], 20___ our total assets were approximately $[    ] million, of which, our investments comprised $[    ] million at fair value and $[    ] million at cost. Our investments at fair value were comprised of our debt investments, warrant portfolio and equity investments valued at approximately $[    ] million, $[    ] million and $[    ] million, respectively, or [    ]%, [    ]% and [    ]% of total investments, respectively. Our[    ], 20___ total investments at value in foreign companies were approximately $[    ] million or [    ]% of total assets. During the [    ]-month periods ended [    ], 20___, we made debt commitments totaling $[    ] million and $[    ] million, respectively, and funded approximately $[    ] million and $[    ] million, respectively. During the[    ]-month period ended [    ], 20___, we made and funded equity commitments of approximately $[    ] and $[    ] million to [    ] and[    ] portfolio companies, respectively. Debt commitments for the nine months ended [    ], 20___ included commitments of approximately $[    ] million to[    ]new portfolio companies and $[    ] million to [    ] existing portfolio companies. Since inception through [    ], 20___, we have made debt and equity commitments of approximately $[    ] billion to our portfolio companies.

We also make investments in qualifying small businesses through two wholly-owned, small business investment company (“SBIC”) subsidiaries, Hercules Technology II, L.P. (“HT II”) and Hercules Technology III, L.P. (“HT III”). As SBICs, HT II and HT III are subject to a variety of regulations concerning, among other things, the size and nature of the companies in which they may invest and the structure of those investments. As of [    ], 20___, we held investments in HT II in [    ] companies with a fair value of approximately $[    ] million. HT II’s portfolio companies accounted for approximately [    ]% of our total portfolio at [    ], 20___. As of [    ], 20___, we held investments in HT III in [    ] companies with a fair value of approximately $[    ] million. HT III’s portfolio accounted for approximately [    ]% of our total portfolio at [    ], 20___.

In aggregate, HT II and HT III held approximately $[    ] million in assets and accounted for approximately [    ]% of our total assets prior to consolidation at [    ], 20___.

We primarily finance privately-held companies backed by leading venture capital and private equity firms and also may finance certain select publicly-traded companies that lack access to public capital or are sensitive to equity ownership dilution. As of [    ], 20___, our proprietary SQL-based database system included over [    ] technology-related companies and approximately [    ] venture capital, private equity sponsors/investors, as well as various other industry contacts. Our principal executive office is located in Silicon Valley, and we have additional offices in Boston, MA, Boulder, CO and McLean, VA. Our goal is to be the leading structured debt financing provider of choice for venture capital and private equity backed technology-related companies requiring sophisticated and customized financing solutions. Our strategy is to evaluate and invest in a broad range of ventures active in the technology, clean technology and life science industries and to offer a full suite of growth capital products up and down of the capital structure. We invest primarily in structured debt 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 rights to purchase common or preferred stock. Our structured debt with warrants investments will typically be secured by select or all of the assets of the portfolio company.

We focus our investments in companies active in technology industry sub-sectors characterized by products or services that require advanced technologies, including, but not limited to, computer software and hardware, networking systems, semiconductors, semiconductor capital equipment, information technology infrastructure or services, Internet consumer and business services, telecommunications, telecommunications equipment, media and life sciences. Within the life sciences sub-sector, we focus on medical devices, bio-pharmaceutical, drug discovery, drug delivery, health care services and information systems companies. Within the clean technology sub-sector, we

Table of Contents

focus on sustainable and renewable energy technologies and energy efficiency and monitoring technologies. We refer to all of these companies as “technology-related” companies and intend, under normal circumstances, to invest at least 80% of the value of our assets in such businesses.

Our primary business objectives are to increase our net income, net operating income and net asset value by investing in structured debt with warrants and equity of venture capital and private equity backed technology-related companies with attractive current yields and the potential for equity appreciation and realized gains. Our structured debt investments typically include warrants or other equity interests, giving us the potential to realize equity-like returns on a portion of our investments. Our equity ownership in our portfolio companies may represent a controlling interest. In some cases, we receive the right to make additional equity investments in our portfolio companies in connection with future equity financing rounds. Capital that we provide directly to venture capital and private equity backed technology-related companies is generally used for growth, and general working capital purposes as well as in select cases for acquisitions or recapitalizations.

Our portfolio is comprised of, and we anticipate that our portfolio will continue to be comprised of, investments in technology-related companies at various stages of development. Consistent with regulatory requirements, we invest primarily in United States based companies and to a lesser extent in foreign companies. See “Regulation—Qualifying Assets” in the accompanying prospectus. Since 2007, our investing emphasis has been primarily on private companies following or in connection with a subsequent institutional round of equity financing, which we refer to as expansion-stage companies and private companies in their later rounds of financing and certain public companies, which we refer to as established-stage companies and lower middle market companies. We have also historically focused our investment activities in private companies following or in connection with the first institutional round of financing, which we refer to as emerging-growth companies.

Beginning in the fall of 2008, the global economy entered a financial crisis and recession. Volatile capital and credit markets, declining business and consumer confidence and increased unemployment precipitated a continuing economic slowdown. Although there have been signs of recovery in many regions, economic weakness could continue or worsen. For example, the current U.S. debt ceiling and budget deficit concerns, together with signs of deteriorating sovereign debt conditions in Europe, have increased the possibility of credit-rating downgrades and economic slowdowns. Although U.S. lawmakers passed legislation to raise the federal debt ceiling, Standard & Poor’s Ratings Services lowered its long-term sovereign credit rating on the United States from “AAA” to “AA+” on August 5, 2011. The impact of this or any further downgrades to the U.S. government’s sovereign credit rating, or its perceived creditworthiness, and the impact of the current crisis in Europe with respect to the ability of certain European Union countries to continue to service their sovereign debt obligations is inherently unpredictable and could adversely effect the U.S. and global financial markets and economic conditions. During market distruptions, we may have difficulty raising debt or equity capital especially as a result of regulatory constraints. There can be no assurance that governmental or other measures to aid economic recovery will be effective.

As of [    ], 20___, our investment professionals, including Manuel A. Henriquez, our co-founder, Chairman, President and Chief Executive Officer, are currently comprised of [    ] professionals who have, on average, more than [    ] years of experience in venture capital, structured finance, commercial lending or acquisition finance with the types of technology-related companies that we are targeting. We believe that we can leverage the experience and relationships of our management team to successfully identify attractive investment opportunities, underwrite prospective portfolio companies and structure customized financing solutions.

Our Market Opportunity

We believe that technology-related companies compete in one of the largest and most rapidly growing sectors of the U.S. economy and that continued growth is supported by ongoing innovation and performance improvements in technology products as well as the adoption of technology across virtually all industries in response to competitive pressures. We believe that an attractive market opportunity exists for a specialty finance company focused primarily on investments in structured debt with warrants in technology-related companies for the following reasons:

Table of Contents

Technology-Related Companies are Underserved by Traditional Lenders. We believe many viable technology-related companies backed by financial sponsors have been unable to obtain sufficient growth financing from traditional lenders, including financial services companies such as commercial banks and finance companies, particularly due to the recent credit market dislocation and because traditional lenders have continued to consolidate and have adopted a more risk-averse approach to lending. More importantly, we believe traditional lenders are typically unable to underwrite the risk associated with financial sponsor-backed emerging-growth or expansion-stage companies effectively.

The unique cash flow characteristics of many technology-related companies include significant research and development expenditures and high projected revenue growth thus often making such companies difficult to evaluate from a credit perspective. In addition, the balance sheets of emerging-growth and expansion-stage companies often include a disproportionately large amount of intellectual property assets, which can be difficult to value. Finally, the speed of innovation in technology and rapid shifts in consumer demand and market share add to the difficulty in evaluating technology-related companies.

Due to the difficulties described above, we believe traditional lenders are generally refraining from entering the structured mezzanine marketplace, instead preferring the risk-reward profile of asset based lending. Traditional lenders generally do not have flexible product offerings that meet the needs of technology-related companies. The financing products offered by traditional lenders typically impose on borrowers many restrictive covenants and conditions, including limiting cash outflows and requiring a significant depository relationship to facilitate rapid liquidation.

Unfulfilled Demand for Structured Debt Financing to Technology-Related Companies. Private debt capital in the form of structured debt financing from specialty finance companies continues to be an important source of funding for technology-related companies. We believe that the level of demand for structured debt financing is a function of the level of annual venture equity investment activity. In the first [    ] months of 20        , venture capital-backed companies received, in approximately [    ] transactions, equity financing in an aggregate amount of approximately $[    ] billion, representing a [    ]% increase from the same period of the preceding year, as reported by Dow Jones VentureSource. In addition, overall, the median round size during the three-month periods ended [    ], 20         and 20         was approximately $[    ] million and $[    ] million, respectively. We believe the larger number of companies provides us a greater opportunity to provide debt financing to these venture backed companies. Overall, seed- and first-round deals made up [    ]% of the deal flow in the three months ended [    ], 20         and later-stage deals made up roughl y[    ]% of the deal activity in the quarter.

We believe that demand for structured debt financing is currently under served, in part because of the credit market collapse in 2008 and the resulting exit of debt capital providers to technology-related companies. The venture capital market for the technology-related companies in which we invest has been active and is continuing to show signs of increased investment activity. In addition, lending requirements of traditional lenders have recently become more stringent due to the significant write-offs in the financial services sector, the re-pricing of credit risk in the broadly syndicated market and the financial turmoil affecting the banking system and financial market, which have negatively impacted the debt and equity capital market in the United States and most other markets. At the same time, the venture capital market for the technology-related companies in which we invest has continued to be active. Therefore, to the extent we have capital available, we believe this is an opportune time to be active in the structured lending market for technology-related companies.

Structured Debt with Warrants Products Complement Equity Financing From Venture Capital and Private Equity Funds. We believe that technology-related companies and their financial sponsors will continue to view structured debt securities as an attractive source of capital because it augments the capital provided by venture capital and private equity funds. We believe that our structured debt with warrants product provides access to growth capital that otherwise may only be available through incremental investments by existing equity investors. As such, we provide portfolio companies and their financial sponsors with an opportunity to diversify their capital

Table of Contents

sources. Generally, we believe emerging-growth and expansion-stage companies target a portion of their capital to be debt in an attempt to achieve a higher valuation through internal growth. In addition, because financial sponsor-backed companies have potentially reached a more mature stage prior to reaching a liquidity event, we believe our investments provide the debt capital needed to grow or recapitalize companies during the extended period prior to liquidity events.

Our Business Strategy

Our strategy to achieve our investment objective includes the following key elements:

Leverage the Experience and Industry Relationships of Our Management Team and Investment Professionals. We have assembled a team of experienced investment professionals with extensive experience as venture capitalists, commercial lenders and originators of structured debt and equity investments in technology-related companies. Our investment professionals have, on average, more than [    ] years of experience as equity investors in, and/or lenders to, technology-related companies. Our team members have originated structured debt, structured debt with warrants and equity investments in over [    ] technology-related companies, representing over $[    ] billion in commitments from inception through [    ], 20         and have developed a network of industry contacts with investors and other participants within the venture capital and private equity communities. In addition, members of our management team also have operational, research and development and finance experience with technology- related companies. We have established contacts with leading venture capital and private equity fund sponsors, public and private companies, research institutions and other industry participants, which should enable us to identify and attract well-positioned prospective portfolio companies.

We concentrate our investing activities generally in industries in which our investment professionals have investment experience. We believe that our focus on financing technology-related companies will enable us to leverage our expertise in structuring prospective investments, to assess the value of both tangible and intangible assets, to evaluate the business prospects and operating characteristics of technology-related companies and to identify and originate potentially attractive investments with these types of companies.

Mitigate Risk of Principal Loss and Build a Portfolio of Equity-Related Securities. We expect that our investments have the potential to produce attractive risk adjusted returns through current income, in the form of interest and fee income, as well as capital appreciation from equity-related securities. We believe that we can mitigate the risk of loss on our debt investments through the combination of loan principal amortization, cash interest payments, relatively short maturities, security interests in the assets of our portfolio companies, and, on select investments, covenants requiring prospective portfolio companies to have certain amounts of available cash and the continued support from a venture capital or private equity firm at the time we make our investment.

Historically our structured debt investments to technology-related companies, typically include warrants or other equity interests, giving us the potential to realize equity-like returns on a portion of our investment. In addition, in some cases, we receive the right to make additional equity investments in our portfolio companies in connection with future equity financing rounds. We believe these equity interests will create the potential for meaningful long-term capital gains in connection with the future liquidity events of these technology-related companies.

Provide Customized Financing Complementary to Financial Sponsors’ Capital. We offer a broad range of investment structures and possess expertise and experience to effectively structure and price investments in technology-related companies. Unlike many of our competitors that only invest in companies that fit a specific set of investment parameters, we have the flexibility to structure our investments to suit the particular needs of our portfolio companies. We offer customized financing solutions ranging from senior debt to equity capital, with a focus on structured debt with warrants.

We use our relationships in the financial sponsor community to originate investment opportunities. Because venture capital and private equity funds typically invest solely in the equity securities of their portfolio companies, we believe that our debt investments will be viewed as an attractive and complementary source of capital, both by the portfolio company and by the portfolio company’s financial sponsor. In addition, we believe that many venture capital and private equity fund sponsors encourage their portfolio companies to use debt financing for a portion of their capital needs as a means of potentially enhancing equity returns, minimizing equity dilution and increasing valuations prior to a subsequent equity financing round or a liquidity event.

Table of Contents

Invest at Various Stages of Development. We provide growth capital to technology-related companies at all stages of development, from emerging-growth companies, to expansion-stage companies and established-stage companies, including select publicly listed companies and select lower middle market companies. We believe that this provides us with a broader range of potential investment opportunities than those available to many of our competitors, who generally focus their investments on a particular stage in a company’s development. Because of the flexible structure of our investments and the extensive experience of our investment professionals, we believe we are well positioned to take advantage of these investment opportunities at all stages of prospective portfolio companies’ development.

Benefit from Our Efficient Organizational Structure. We believe that the perpetual nature of our corporate structure enables us to be a long-term partner for our portfolio companies in contrast to traditional mezzanine and investment funds, which typically have a limited life. In addition, because of our access to the equity markets, we believe that we may benefit from a lower cost of capital than that available to private investment funds. We are not subject to requirements to return invested capital to investors nor do we have a finite investment horizon. Capital providers that are subject to such limitations are often required to seek a liquidity event more quickly than they otherwise might, which can result in a lower overall return on an investment.

Deal Sourcing Through Our Proprietary Database. We have developed a proprietary and comprehensive structured query language-based (SQL) database system to track various aspects of our investment process including sourcing, originations, transaction monitoring and post-investment performance. As of [    ], 20        , our proprietary SQL-based database system included over [    ] technology-related companies and over [    ] venture capital, private equity sponsors/investors, as well as various other industry contacts. This proprietary SQL system allows us to maintain, cultivate and grow our industry relationships while providing us with comprehensive details on companies in the technology-related industries and their financial sponsors.

Recent Developments

[Insert description of recent developments at time of offering.]

Table of Contents

SPECIFIC TERMS OF THE NOTES AND THE OFFERING

This prospectus supplement sets forth certain terms of the Notes that we are offering pursuant to this prospectus supplement and supplements the accompanying prospectus that is attached to the back of this prospectus supplement. This section outlines the specific legal and financial terms of the Notes. You should read this section together with the more general description of the Notes in the accompanying prospectus under the heading “Description of Our Debt Securities” before investing in the Notes. Capitalized terms used in this prospectus supplement and not otherwise defined shall have the meanings ascribed to them in the accompanying prospectus or in the indenture governing the Notes.

Table of Contents

Table of Contents

Table of Contents

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 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. In such case, our net asset value and the trading price of our common stock 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 us as well as those factors generally associated with an investment company with investment objectives, investment policies, capital structure or trading markets similar to ours.

[The Notes will be unsecured and therefore will be effectively subordinated to any secured indebtedness we may incur.

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 outstanding as of the date of this prospectus supplement or that they 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 [            ], we had $[            ] million in outstanding indebtedness that is senior to the Notes. Certain amounts of this indebtedness are secured by certain of our assets and the indebtedness thereunder is therefore effectively senior to the Notes to the extent of the value of such assets.]

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

The Notes are obligations exclusively of Hercules Technology Growth Capital, Inc. and not of any of our subsidiaries. None of our subsidiaries is a guarantor of the Notes. Except to the extent we are a creditor with recognized claims against our subsidiaries, all claims of creditors, including trade creditors, and holders of preferred stock, if any, of our subsidiaries will have priority over our claims (and therefore the claims of our creditors, including holders of the Notes) with respect to the assets of such subsidiaries. Even if we were 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 subordinated structurally 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. All of the existing indebtedness of our subsidiaries 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 governing the Notes will be issued will contain limited protection for holders of the Notes.

The indenture governing 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:

Table of Contents

of ours that is guaranteed by one or more of our subsidiaries and [which therefore] is structurally senior to the Notes and (4) securities, indebtedness or obligations issued or incurred by our subsidiaries that would be senior to our equity interests in our subsidiaries and therefore rank structurally senior to the Notes with respect to the assets of our subsidiaries;

In addition, 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 except as required by the 1940 Act.

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. 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.

An active trading market for the Notes may not develop, which could limit the market price of the Notes or your ability to sell them. [Because one or more rating agencies have assigned the Notes a non-investment grade rating, the Notes may be subject to greater price volatility than similar securities without such a rating.]

The Notes are a new issue of debt securities for which there currently is no trading market. [Although we expect the Notes to be listed on                     ,] we cannot provide any assurances that an active trading market will develop for the Notes or that you will be able to sell your Notes. 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. [Moreover, because one or more rating agencies have assigned the Notes a non-investment grade rating, the Notes may be subject to greater price volatility than securities of similar maturity without such a non-investment grade rating.] 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 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, 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.

[Insert any additional relevant risk factors not included in base prospectus.]

Table of Contents

SPECIAL NOTE REGARDING 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 Technology Growth 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 words. 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 and our outlook on the economy and its effect on venture capital. In light of these and other uncertainties, the inclusion of a projection or forward-looking statement in this prospectus supplement and the accompanying 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:

Table of Contents

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 “Risk Factors” in both this prospectus supplement and the accompanying prospectus. You should not place undue reliance on these forward-looking statements. The forward-looking statements made in this prospectus supplement and the accompanying prospectus relate only to events as of the date on which the statements are made. The forward-looking statements contained herein are excluded from the safe harbor protection provided by Section 27A of the Securities Act of 1933.

This prospectus supplement and the accompanying prospectus contain third-party estimates and data regarding valuations of venture capital-backed companies. This data was reported by Dow Jones VentureSource, an independent venture capital industry research company which we refer to as VentureSource. VentureSource is commonly relied upon as an information source in the venture capital industry. Although we have not independently verified any such data, we believe that the industry information contained in such releases and data tables and included in this prospectus supplement and the accompanying prospectus is reliable.

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 common stock could be materially adversely affected.

Table of Contents

USE OF PROCEEDS

We estimate that net proceeds we will receive from the sale of $         aggregate principal amount of Notes in this offering will be approximately $         million (or approximately $         million if the underwriters fully exercise their overallotment option), after deducting the underwriting discounts and commissions of $         million (or approximately $         million if the underwriters fully exercise their overallotment option) payable by us and estimated offering expenses of approximately $         payable by us.

We expect to use the net proceeds from this offering to fund investments in debt and equity securities in accordance with our investment objective and for other general corporate purposes.

We anticipate that substantially all of the net proceeds from this offering will be used as described above within twelve months, but in no event longer than two years. Pending such uses and investments, we will invest the net proceeds 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 objective may be limited to the extent that the net proceeds of any offering, pending full investment, are held in lower yielding short-term instruments.

Table of Contents

RATIO OF EARNINGS TO FIXED CHARGES

[Insert information required by Item 503(d) of Regulation S-K at time of offering.]

Table of Contents

CAPITALIZATION

The following table sets forth (i) our actual capitalization as of ,         20 , and (ii) our capitalization as adjusted to give effect to the sale of $         aggregate principal amount of Notes in this offering based on the public offering price of $         per Note, after deducting the underwriting discounts and commissions of $         million payable by us and estimated offering expenses of approximately $         payable by us.

Table of Contents

UNDERWRITING

We are offering the Notes described in this prospectus supplement and the accompanying prospectus through a number of underwriters.         and         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 agreed to purchase the aggregate principal amount of Notes listed next to its name in the following table:

The underwriters are committed to purchase all of the Notes offered by us if they purchase any Notes. The underwriting agreement also provides that if an underwriter defaults, the purchase commitments of non-defaulting underwriters may also be increased or this offering may be terminated.

[Over-Allotment Option

The underwriters have an option to buy up to an additional $            aggregate principal amount of the Notes from us to cover sales of Notes by the underwriters which exceed the amount of Notes specified in the table above. The underwriters have          days from the date of this prospectus supplement to exercise this overallotment option. If any Notes are purchased with this overallotment option, the underwriters will purchase Notes in approximately the same proportion as shown in the table above. If any additional Notes are purchased, the underwriters will offer the additional Notes on the same terms as those on which the shares are being offered.]

The underwriters propose to offer the Notes directly to the public at the public offering price set forth on the cover page of this prospectus supplement and to certain dealers at that price less a concession not in excess of $            per Note. Any such dealers may resell Notes to certain other brokers or dealers at a discount of up to $            per Note from the public offering price. After the public offering of the Notes, the offering price and other selling terms may be changed by the underwriters. Sales of Notes made outside of the United States may be made by affiliates of the underwriters. The representatives have advised us that the underwriters do not intend to confirm discretionary sales in excess of % of the Notes offered in this offering.

Commissions and Discounts

The underwriting fee is equal to % of the public offering price per Note. The underwriting fee is $ per Note. The following table shows the per Note and total underwriting discounts and commissions to be paid to the underwriters assuming both no exercise and full exercise of the underwriters’ option to purchase additional Notes.

We estimate that the total expenses of this offering, including registration, filing and listing fees, printing fees and legal and accounting expenses, but excluding the underwriting discounts and commissions, will be approximately $            , or approximately $            per Note excluding the over-allotment and approximately $            per Note including the over-allotment.

Table of Contents

[Lock-Up Agreements

During the period from the date of this prospectus supplement continuing through the date days after the date of this prospectus, we, our officers and directors have agreed with the representatives of the underwriters, subject to certain exceptions, not to:

Moreover, if (1) during the last 17 days of such    -day restricted period, we issue an earnings release or material news or a material event relating to us occurs or (2) prior to the expiration of such    -day restricted period, we announce that we will release earnings results or become aware that material news or a material event will occur during the 16-day period beginning on the last day of such    -day restricted period, the restrictions described above shall continue to apply until the expiration of the 18-day period beginning on the date of issuance of the earnings release or the occurrence of the material news or material event, as the case may be, unless the representatives of the underwriters waive, in writing, such extension.]

Price Stabilizations and Short Positions

In connection with this offering,            and            , on behalf of the underwriters, may purchase and sell Notes in the open market. These transactions may include short sales, syndicate covering transactions and stabilizing transactions. Short sales involve sales by the underwriters of securities in excess of the number of securities required to be purchased by the underwriters in the offering, which creates a syndicate short position. “Covered” short sales are sales of securities made in an amount up to the number of securities represented by the underwriters’ over-allotment option. Transactions to close out the covered syndicate short involve either purchases of such securities in the open market after the distribution has been completed or the exercise of the over-allotment option. In determining the source of securities to close out the covered syndicate short position, the underwriters may consider the price of securities available for purchase in the open market as compared to the price at which they may purchase securities through the over-allotment option. The underwriters may also make “naked” short sales, or sales in excess of the over-allotment option. The underwriters must close out any naked short position by purchasing securities in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the securities in the open market after pricing that could adversely affect investors who purchase in this offering. Stabilizing transactions consist of bids for or purchases of securities in the open market while this offering is in progress for the purpose of fixing or maintaining the price of the securities.

The underwriters also may impose a penalty bid. Penalty bids permit the underwriters to reclaim a selling concession from an underwriter or syndicate member when the underwriters repurchase securities originally sold by that underwriter or syndicate member in order to cover syndicate short positions or make stabilizing purchases.

Any of these activities may have the effect of raising or maintaining the market price of the securities or preventing or retarding a decline in the market price of the securities. As a result, the price of the securities may be higher than the price that might otherwise exist in the open market. The underwriters may conduct these transactions on or otherwise. Neither we nor any of the underwriters makes any representation or prediction as to the direction or magnitude of any effect that the transactions described above may have on the price of our securities. In addition, neither we nor any of the underwriters makes any representation that the underwriters will engage in these transactions. If the underwriters commence any of these transactions, they may discontinue them at any time.

In connection with this offering, the underwriters may engage in passive market making transactions in our securities on                 in accordance with Rule 103 of Regulation M under the Exchange Act during a period before

Table of Contents

the commencement of offers or sales of securities and extending through the completion of distribution. A passive market maker must display its bid at a price not in excess of the highest independent bid of that security. However, if all independent bids are lowered below the passive market maker’s bid, that bid must then be lowered when specified purchase limits are exceeded.

Additional Underwriter Compensation

Certain of the underwriters and their respective affiliates have from time to time performed and may in the future perform various commercial banking, financial advisory and investment banking services for us and our affiliates for which they have received or will receive customary compensation. [Describe any specific transactions and compensation related thereto required to be disclosed by applicable law or regulation.]

Sales Outside the United States

No action has been taken in any jurisdiction (except in the United States) that would permit a public offering of the Notes, or the possession, circulation or distribution of this prospectus supplement or accompanying prospectus or any other material relating to us or the Notes in any jurisdiction where action for that purpose is required. Accordingly, our warrants may not be offered or sold, directly or indirectly, and none of this prospectus supplement, the accompanying prospectus or any other offering material or advertisements in connection with our warrants may be distributed or published, in or from any country or jurisdiction except in compliance with any applicable rules and regulations of any such country or jurisdiction.

Each of the underwriters may arrange to sell our Notes offered hereby in certain jurisdictions outside the United States, either directly or through affiliates, where it is permitted to do so.

[Insert applicable legends for jurisdictions in which offers and sales may be made.]

Electronic Delivery

The underwriters may make this prospectus supplement and accompanying prospectus available in an electronic format. The prospectus supplement and accompanying prospectus in electronic format may be made available on a website maintained by any of the underwriters, and the underwriters may distribute such documents electronically. The underwriters may agree with us to allocate a limited number of securities for sale to their online brokerage customers. Any such allocation for online distributions will be made by the underwriters on the same basis as other allocations.

We estimate that our share of the total expenses of this offering, excluding underwriting discounts, will be approximately $            .

We have agreed to indemnify the several underwriters against certain liabilities, including liabilities under the Securities Act.

The addresses of the underwriters are:         .

Table of Contents

UNITED STATES FEDERAL INCOME TAX CONSEQUENCES

[Insert disclosure regarding federal income tax consequences of an investment in the Notes.]

Table of Contents

LEGAL MATTERS

Certain legal matters in connection with the securities offered hereby will be passed upon for us by Sutherland Asbill & Brennan LLP, Washington, DC. Certain legal matters in connection with the securities offered hereby will be passed upon for the underwriters by .

INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

The financial statements as of                     ,          and for the year ended December 31,         , included in this prospectus, and the effectiveness of internal control over financial reporting as of December 31, 20     have been audited by PricewaterhouseCoopers LLP, an independent registered public accounting firm, as stated in their report appearing herein.

Certain of our audited consolidated financial statements included in this prospectus have been so included in reliance upon the report of Ernst & Young LLP, our former independent registered public accountants. Ernst & Young LLP’s principal business address is 560 Mission Street, San Francisco, CA 94105.

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 shares of common stock offered by this prospectus supplement and the accompanying prospectus. The registration statement contains additional information about us and our shares of common stock being offered by this prospectus supplement and the accompanying prospectus.

We are required to file with or submit to the SEC annual, quarterly and current periodic reports, proxy statements and other information meeting the informational requirements of the Exchange Act. You may inspect and copy these reports, proxy statements and other information, as well as the registration statement and related exhibits and schedules, at the Public Reference Room of the SEC in Washington, D.C. 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 site that contains reports, proxy and information statements and other information filed electronically by us with the SEC

Table of Contents

which are available on the SEC’s 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 to the SEC’s Public Reference Section, Washington, D.C. 20549. The information is available free of charge by contacting us at Hercules Technology Growth Capital, Inc., 400 Hamilton Avenue, Suite 310, Palo Alto, CA 94301, or by calling us collect at (650) 289-3060 or on our website at www.herculestech.com.