UMC Announces Share Buyback Exceeding 300 Million TWD

Announcement Date: May 16, 2026 Declaration Date: May 15, 2026 Declaration Time: 14:30:28 Company Code: 2303 Company Name: UMC Subject: Announcement of share buyback exceeding 300 million New Taiwan Dollars. Clause Met: Article 35 Date of Event: May 15, 2026 Explanation: 1. Date on which cumulative repurchased shares reached 2% of total issued shares or amount exceeded 300 million TWD: May 15, 2026. 2. Number of shares repurchased this time: 3,780,000 shares. 3. Total amount of shares repurchased this time: 406,598,693 TWD. 4. Average price per share repurchased: 107.57 TWD. 5. Cumulative number of own shares held during the buyback period: 20,531,000 shares. 6. Ratio of own shares held to total issued shares during the buyback period: 0.16%. 7. Other remarks: None.