SEC Form 424B3 filed by Horizon Technology Finance Corporation

Filed Pursuant to Rule 424(b)(3)

Registration No. No. 333-290114

HORIZON TECHNOLOGY FINANCE CORPORATION

MONROE CAPITAL CORPORATION

Supplement No. 1, dated March 5, 2026, to the

Joint Proxy Statement/Prospectus, dated January 16, 2026

This supplement contains information that amends, supplements or modifies certain information contained in the combined prospectus of Horizon Technology Finance Corporation (“HRZN”), and definitive joint proxy statement of HRZN and Monroe Capital Corporation (“MRCC”), dated January 16, 2026 (the “Joint Proxy Statement/Prospectus”). This supplement is part of, and should be read in conjunction with, the Joint Proxy Statement/Prospectus. The Joint Proxy Statement/Prospectus has been filed with the U.S. Securities and Exchange Commission (the “SEC”), and is available free of charge at www.sec.gov or by calling HRZN at (860) 676-8654, or by writing to HRZN at 312 Farmington Avenue, Farmington, Connecticut 06032, Attention: Investor Relations, or by calling MRCC at (312) 258-8300, or by writing to MRCC at 155 North Wacker Drive, 35th Floor, Chicago, Illinois 60606, Attention: Investor Relations. Capitalized terms used herein but not defined shall have the meanings ascribed to such terms in the Joint Proxy Statement/Prospectus.

INCORPORATION BY REFERENCE FOR HRZN

This supplement incorporates by reference the documents set forth below that have previously been filed with the SEC:

INCORPORATION BY REFERENCE FOR MRCC

This supplement incorporates by reference the documents set forth below that have previously been filed with the SEC:

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