Winbond Announces Change in Accounting Estimate Effective July 1, 2026

1. Board Resolution Date: 06/12/2026 2. Nature of Change: Adjustment in the estimated depreciation period for Module A machinery and associated pipeline facilities at the Kaohsiung plant 3. Reason for Change: In accordance with Paragraph 6 of the Rules Governing the Preparation of Financial Reports by Securities Issuers and IAS 16, enterprises are required to periodically review the useful lives of assets so that the carrying value of equipment more accurately reflects its actual economic benefits. Winbond commissioned Chung Hua Credit Information Corporation to re-evaluate the economic life of the equipment. As a result, the depreciation period for Module A machinery and utility pipeline facilities at the Kaohsiung plant has been adjusted to 6 years, and the certified public accountant has issued a review opinion on the reasonableness of this change. 4. Retroactive Application of New Accounting Policy: Not applicable 5. Affected Items and Actual Impact Amount for the Prior Year: None 6. Actual Impact on Opening Retained Earnings for the Prior Year: None 7. Rationale and Necessity for Changing Accounting Policy or Estimate After the Start of the Accounting Year: Due to recent changes in product mix and market demand, memory products are evolving toward customization, high performance, and low power consumption. The proportion of customized memory solutions continues to increase, leading to higher frequencies of technological iteration and process conversion. Additionally, the company has adopted a highly flexible production model and continues to optimize processes and implement digital management, resulting in more diverse equipment usage patterns and changes in the consumption pattern of economic benefits. Therefore, a re-evaluation of the useful life of related equipment is necessary to more reasonably reflect the actual economic benefits of the assets. 8. Explanation of Why Retroactive Application Is Not Feasible When Determining Impact Amounts Is Not Practicable, How and When the Accounting Change Is Applied: Not applicable 9. Auditor’s Opinion on the Impact of the Accounting Change on the Audit Opinion for the Prior Year When Determining the Impact Amount Is Not Practicable: Not applicable 10. Auditor’s Opinion on the Reasonableness of the Change: According to the review opinion issued by the auditor, no significant unreasonable matters or non-compliance with relevant regulations were found in the accounting estimate change. 11. Dissenting or Reserved Opinions from Independent Directors: Not applicable 12. Mitigation Measures: None 13. Other Matters to Be Disclosed: The above accounting estimate change will be effective from July 1, 2026. This matter was approved by the Audit Committee and Board of Directors on June 12, 2026.