**Exhibit 12.1****CERTIFICATION OF OUR CHIEF EXECUTIVE OFFICER**I, Chi-Wen Tsai, certify that:1. I have reviewed this annual report on Form 20-F of Siliconware Precision Industries Co., Ltd.(the “Company”); 2. Based on my knowledge, this report does not contain any untrue statement of a material factor omit to state a material fact necessary to make the statements made, in light of thecircumstances under which such statements were made, not misleading with respect to the periodcovered by this report; 3. Based on my knowledge, the financial statements, and other financial information included inthis report, fairly present in all material respects the financial condition, results ofoperations and cash flows of the Company as of, and for, the periods presented in this report; 4. The Company’s other certifying officer and I are responsible for establishing and maintainingdisclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e))and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and15d-15(f)) for the Company and have: (a) Designed such disclosure controls and procedures, or caused such disclosure controlsand procedures to be designed under our supervision, to ensure that material informationrelating to the Company, including its consolidated subsidiaries, is made known to us byothers within those entities, particularly during the period in which this report is beingprepared;  (b) Designed such internal control over financial reporting, or caused such internalcontrol over financial reporting to be designed under our supervision, to providereasonable assurance regarding the reliability of financial reporting and the preparationof financial statements for external purposes in accordance with generally acceptedaccounting principles;  (c) Evaluated the effectiveness of the Company’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of the disclosure controlsand procedures, as of the end of the period covered by this report based on suchevaluation; and  (d) Disclosed in this report any change in the Company’s internal control over financialreporting that occurred during the period covered by this report that has materiallyaffected, or is reasonably likely to materially affect, the Company’s internal control overfinancial reporting.5. The Company’s other certifying officer and I have disclosed, based on our most recentevaluation of internal control over financial reporting, to the Company’s auditors and theaudit committee of the Company’s board of directors (or persons performing the equivalentfunction): (a) All significant deficiencies and material weaknesses in the design or operation ofinternal controls over financial reporting, which are reasonably likely to adversely affectthe Company’s ability to record, process, summarize and report financial information; and  (b) Any fraud, whether or not material, that involves management or other employees whohave a significant role in the Company’s internal controls over financial reporting.Date:June 20, 2007         By:                                  /s/ Chi-Wen Tsai    Name:  Chi-Wen Tsai    Title:  Chief Executive Officer