United Microelectronics Corp

www.umc.com Exhibit Exhibit Description 99.1 Announcement on 2026/09/03: UMC will attend investor conferences on 2026/09/10 99.2 Announcement on 2026/09/03: UMC will attend investor conferences on 2026/09/14~2026/09/15 99.3 Announcement on 2026/09/04: August Revenue

Exhibit 99.1 UMC will attend investor conferences on 2026/09/10 1. Date of institutional investor conference: 2026/09/10 2. Time of institutional investor conference: 09:30 PM 3. Location of institutional investor conference: New York Hilton Midtown 4. Outline of institutional investor conference: The Company will attend the "2026 GEMs Conference", held by Citi. 5. Any other matters that need to be specified: None

Exhibit 99.2 UMC will attend investor conferences on 2026/09/14~2026/09/15 1. Date of institutional investor conference: 2026/09/14~2026/09/15 2. Time of institutional investor conference: 09:00 AM 3. Location of institutional investor conference: W Hotel Taipei 4. Outline of institutional investor conference: The Company will attend the "Taiwan Summit 2026", held by UBS. 5. Any other matters that need to be specified: None

Exhibit 99.3 United Microelectronics Corporation September 4, 2026 This is to report the changes or status of 1) Sales volume, 2) Funds lent to other parties, 3) Endorsements and guarantees, and 4) Financial derivative transactions for the period of August 2026. 1) Sales volume (NT$ Thousand)

2) Funds lent to other parties (NT$ Thousand): None

3) Endorsements and guarantees (NT$ Thousand): None

a Not under hedging accounting: NT$ thousand UMC

Financial instruments Option Forwards IRS

Net profit (loss) from Fair Value 0 0 10,372 0