Exhibit d.3

NOTICE OF GUARANTEED DELIVERY FOR SHARES OF

COMMON STOCK OF HERCULES TECHNOLOGY GROWTH CAPITAL, INC.

SUBSCRIBED FOR PURSUANT TO THE BASIC SUBSCRIPTION

AND THE OVER-SUBSCRIPTION PRIVILEGE

Hercules Technology Growth Capital, Inc. Rights Offering

As set forth in the Prospectus dated March [    ], 2006 (the “Prospectus”) under “Terms of the Offer—Methods for Exercising Rights,” this form or one substantially equivalent hereto may be used as a means of effecting subscription and payment for all shares of Hercules Technology Growth Capital, Inc. shares of common stock (the “Shares”) subscribed for by exercise of transferable rights (“Rights”) pursuant to the basic subscription and the over-subscription privilege. Such form may be delivered by hand or sent by facsimile transmission, overnight courier or mail to the Subscription Agent and must be received prior to 5:00 p.m. New York City time on April [    ], 2006 (the “Expiration Date”) or, if the offer is extended, by the close of business two business days prior to the extended Expiration Date. The terms and conditions of the offer set forth in the Prospectus are incorporated by reference herein.

The Subscription Agent is:

AMERICAN STOCK TRANSFER & TRUST COMPANY

DELIVERY OF THIS INSTRUMENT TO AN ADDRESS, OR TRANSMISSION OF

INSTRUCTIONS VIA A TELECOPY OR FACSIMILE NUMBER, OTHER THAN AS SET

FORTH ABOVE, DOES NOT CONSTITUTE A VALID DELIVERY.

The broker-dealer, trust company, bank or other nominee that completes this form must communicate the guarantee and the number of Shares subscribed for under both the basic subscription and the over-subscription privilege to the Subscription Agent and must deliver this Notice of Guaranteed Delivery guaranteeing delivery of (i) payment in full for all subscribed Shares and (ii) a properly completed and executed subscription certificate to the Subscription Agent prior to 5:00 p.m., New York City time, on the Expiration Date. The Subscription

-1-

Certificate and full payment must then be delivered to the Subscription Agent by the close of business on April [    ], 2006, which is the third business day after the Expiration Date, unless extended by Hercules. Failure to do so will result in a forfeiture of the Rights.

GUARANTEE

The undersigned, a broker-dealer, trust company, bank or other nominee, guarantees delivery of payment to the Subscription Agent by the close of business (5:00 p.m., New York City time) on the close of business on the third business day after the Expiration Date (April [    ], 2006, unless extended by the Fund) of (i) a properly completed and duly executed subscription certificate and (ii) payment of the full estimated subscription price of $[    ] per share for the shares subscribed for in the basic subscription and any additional shares subscribed for pursuant to the over-subscription privilege, if applicable, as subscription for such shares is indicated herein or in the Subscription Certificate.

Method of Delivery of Rights (circle one):

-2-

Please note that if you are guaranteeing for over-subscription Shares and are a DTC participant, you must also execute and forward to American Stock Transfer & Trust Company a nominee holder over-subscription certificate.

-3-