【Formosa Plastics】Announcement of Additional Investment in Formosa Tokuyama Advanced Chemicals Co., Ltd.

1. Subject: Equity of Formosa Tokuyama Advanced Chemicals. 2. Date of occurrence: 2026/5/28. 3. Board approval date: 2026/5/28. 5. Transaction volume: 50,000,000 shares at NT$10 per share, total NT$500,000,000. 6. Counterparty: Formosa Tokuyama Advanced Chemicals (an affiliate in which the company holds 50%). 7. Reason: Participation in cash capital increase based on the 50% shareholding ratio. 11. Payment terms: Based on the capital requirements of the subsidiary. 14. Cumulative holdings: 157,204,050 shares (50%). 17. Purpose: Long-term investment. 19. Related party transaction: Yes. 20. Audit committee approval date: 2026/5/26.