SCHEDULE 13D/A 0001666749 XXXXXXXX LIVE 1 Common Stock, no par value 01/30/2026 false 0000836147 596304204 MIDDLEFIELD BANC CORP.

15985 East High Street Middlefield OH 44062

Deborah Sykes 858-756-8300 11682 El Camino Real, Suite 320 San Diego CA 92130 0001666749 N Castle Creek Capital Partners VI, LP WC N DE 0.00 312847.00 0.00 312847.00 312847.00 N 3.9 PN (1) The information set forth in Item 5 of this statement on Schedule 13D is incorporated herein by reference. Y Castle Creek Capital VI LLC AF WC N DE 0.00 312847.00 0.00 312847.00 312847.00 N 3.9 HC OO (1) The information set forth in Item 5 of this statement on Schedule 13D is incorporated herein by reference. Common Stock, no par value MIDDLEFIELD BANC CORP. 15985 East High Street Middlefield OH 44062 This Amendment No. 1 to Schedule 13D (this "Amendment No. 1") amends and supplements the Schedule 13D filed on December 9, 2022 (the "Schedule 13D") with the U.S. Securities and Exchange Commission (the "SEC"), relating to the shares of common stock, no par value per share ("Voting Common Stock"), of Middlefield Banc Corp. (the "Issuer" or the "Company"). Unless specifically amended hereby, the disclosures set forth in the Schedule 13D remain unchanged. Capitalized terms used in this Amendment No. 1 that are not otherwise defined herein have the meanings attributed to them in the Schedule 13D. Item 3 of the Schedule 13D is hereby amended and supplemented by adding the following: Between December 12, 2025 and February 2, 2026 (inclusive), Castle Creek Capital Partners VI, LP ("Fund VI") sold an aggregate of 247,653 shares of Voting Common Stock for proceeds of $8,546,310.15, which represents an amount net of commissions and fees, in various open-market transactions. Following such transactions, Fund VI owns 312,847 shares of Voting Common Stock. Item 5(a) and (b) of the Schedule 13D is hereby amended and supplemented as follows: Fund VI owns 312,847 shares of the Voting Common Stock, which represents approximately 3.9%* of the Voting Common Stock. *This calculation is based on 8,090,067 shares of Voting Common Stock of the Company outstanding as of December 12, 2025, as reported in the Company's proxy statement on Schedule 14A filed with the SEC on December 19, 2025. Fund VI has shared power to vote or direct the vote and shared power to dispose or direct the disposition of the 312,847 shares of Voting Common Stock described above with CCC VI. CCC VI disclaims beneficial ownership of the Voting Common Stock beneficially owned by Fund VI, except to the extent of its pecuniary interest therein. Item 5(c) of the Schedule 13D is hereby amended and supplemented as follows: Except as previously disclosed in the Schedule 13D, Fund VI has engaged in the following open market, broker-assisted transactions with respect to the Voting Common Stock during the last 60 days through the date of the event which requires filing of this Schedule 13D: (i) 16,813 shares of Voting Common Stock sold on December 12, 2025 at a weighted average price of $37.17 per share (in multiple open market, broker-assisted transactions ranging from $36.90 to $37.25 per share, inclusive); (ii) 13,579 shares of Voting Common Stock sold on December 15, 2025 at a weighted average price of $37.00 per share (in multiple open market, broker-assisted transactions ranging from $37.00 to $37.18 per share, inclusive); (iii) 5,627 shares of Voting Common Stock sold on December 16, 2025 at a weighted average price of $37.01 per share (in multiple open market, broker-assisted transactions ranging from $37.00 to $37.095 per share, inclusive); (iv) 5,302 shares of Voting Common Stock sold on December 17, 2025 at a weighted average price of $37.12 per share (in multiple open market, broker-assisted transactions ranging from $37.00 to $37.20 per share, inclusive); (v) 12,909 shares of Voting Common Stock sold on December 18, 2025 at a weighted average price of $37.04 per share (in multiple open market, broker-assisted transactions ranging from $36.90 to $37.27 per share, inclusive); (vi) 200 shares of Voting Common Stock sold on December 19, 2025 at a price of $36.90 per share; (vii) 18,008 shares of Voting Common Stock sold on January 22, 2026 at a weighted average price of $36.12 per share (in multiple open market, broker-assisted transactions ranging from $36.00 to $36.505 per share, inclusive); (viii) 72,772 shares of Voting Common Stock sold on January 30, 2026 at a weighted average price of $33.57 per share (in multiple open market, broker-assisted transactions ranging from $33.50 to $33.79 per share, inclusive); and (ix) 102,443 shares of Voting Common Stock sold on February 2, 2026 at a weighted average price of $33.61 per share (in multiple open market, broker-assisted transactions ranging from $33.30 to $33.98 per share, inclusive). As of February 2, 2026, the Reporting Persons ceased to be the beneficial owner of more than five percent of the Voting Common Stock. Castle Creek Capital Partners VI, LP /s/ Tony Scavuzzo 02/03/2026 Castle Creek Capital VI LLC /s/ Tony Scavuzzo 02/03/2026