On December 15, 2025, GCT Semiconductor Holding, Inc. (the "Company") entered into a Convertible Promissory Note Purchase Agreement (the "Purchase Agreement") with Indigo Capital LP (the "Purchaser"), pursuant to which the Company may issue and sell to the Purchaser convertible promissory notes (the "Convertible Notes") in an aggregate principal amount of up to $20,000,000.

Under the Purchase Agreement, the Purchaser will provide an initial $1,000,000 advance, with additional advances of up to $1,000,000 each available at the Company's request, subject to specified conditions. The Convertible Notes will be issued at a 7% original issue discount, will mature 24 months after issuance, and will not bear interest. The Convertible Notes are convertible into shares of the Company's common stock at a price equal to 90% of the average volume weighted average price of the three trading days prior to conversion, subject to customary beneficial ownership and stock exchange limitations.

The Convertible Notes, together with the shares of common stock issuable upon conversion thereof, are registered for issuance and resale under the Company's Registration Statement on Form S-3 (File No. 333-286316).

The Company may redeem all or a portion of the Convertible Notes after 12 months from issuance, subject to applicable redemption premiums. The Company is also required to maintain an effective registration statement covering the resale of the shares issuable upon conversion of the Convertible Notes and to reserve sufficient shares for such conversions.

Under the Purchase Agreement, the Company has full control over the timing and amount of capital it wishes to raise by selling convertible notes to the Purchaser. Once this debt facility is put in place, the Company has no obligation to sell any notes, and will only issue a put request to sell notes at the right time after considering relevant factors, including at a time when its stock price reaches an optimal level. Accordingly, this debt facility provides with the Company with significant flexibility in its financing plans, while minimizing or eliminating dilution to existing stockholders.

The foregoing description of the Purchase Agreement and the Convertible Notes is qualified in its entirety by reference to the Purchase Agreement and the form of the Convertible Notes, which are filed as Exhibits 10.1 and 4.1, respectively, to this Current Report on Form 8-K and incorporated herein by reference.

The information set forth under Item 1.01 of this Current Report on Form 8-K relating to the issuance of the Convertible Notes and the Company's obligations thereunder is incorporated herein by reference. The Company incurred the obligations under the Convertible Notes upon execution of the Purchase Agreement on December 15, 2025.