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Exhibit

Exhibit Description

99.1 Announcement on 2026/03/12: Represent major subsidiary United Semiconductor (Xiamen) Co., Ltd. to announce important resolutions of the 2026 Shareholders’ Meeting

99.2 Announcement on 2026/03/12: To announce the registration of capital reduction due to cancellation of the RSA

99.3 Announcement on 2026/03/09: the trading and pledge of UMC common shares by directors, executive officers and 10% shareholders of UMC

Represent major subsidiary United Semiconductor (Xiamen) Co., Ltd. to announce important resolutions of the 2026 Shareholders’ Meeting

1. Date of the shareholders meeting: 2026/03/12

2. Important resolutions (1) Profit distribution/ deficit compensation: None

3. Important resolutions (2) Amendments to the corporate charter: None

4. Important resolutions (3) Business report and financial statements:

1)Approved the company’s 2025 Annual Audit Financial Report

5. Important resolutions (4) Elections for board of directors and supervisors: None

6. Important resolutions (5) Any other proposals:

1) Approved the company’s 2026 Annual Operating Budget Proposal

2) Approved to amend the company’s “Asset Acquisition and Disposal Procedures”

7. Any other matters that need to be specified: None

.2

To announce the registration of capital reduction due to cancellation of the RSA

1. Date of the competent authority’s approval of capital reduction: 2026/03/11

2. Date of completion of capitalization change registration: 2026/03/11

3. Effect on the financial statements (including any discrepancy between the amount of paid-in capital and the no. of shares outstanding, and the effect on net worth per share):

(1) Before the capital reduction: The paid-in capital is NT$125,881,563,440; the shares outstanding are 12,588,156,344 shares; book value per share is NT$30.17

(2) After the capital reduction: The paid-in capital is NT$125,785,246,190; the shares outstanding are 12,578,524,619 shares; book value per share is NT$30.19

(Note: Net worth per share was calculated based on the consolidated financial statements for the year of 2025 audited by CPA.)

4. Plan for expected share replacement operations: NA

5. Estimated no. of listed common shares after capital reduction and new issue: NA

6. Estimated no. of listed common shares as a percentage of issued common shares after capital reduction and new issue (No. of common shares after capital reduction/No. of issued common shares): NA

7. Countermeasures for poor circulation of equity if the aforesaid estimated no. of listed common shares does not reach 60 million shares and the percentage does not reach 25% after capital reduction: NA

8. Any other matters that need to be specified: None

.3

United Microelectronics Corporation

For the month of February, 2026

This is to report 1) the trading of directors, executive officers and 10% shareholders of United Microelectronics Corporation (“UMC”) (NYSE: UMC); 2) the pledge and clear of pledge of UMC common shares by directors, executive officers and 10% shareholders of UMC;