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                                                                    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 annual report does not contain any untrue
      statement of a material fact or omit to state a material fact necessary to
      make the statements made, in light of the circumstances under which such
      statements were made, not misleading with respect to the period covered by
      this annual report;

3.    Based on my knowledge, the financial statements, and other financial
      information included in this annual report, fairly present in all material
      respects the financial condition, results of operations and cash flows of
      the Company as of, and for, the periods presented in this annual report;

4.    The Company's other certifying officer and I are responsible for
      establishing and maintaining disclosure controls and procedures (as
      defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the Company and
      have:

      (a)   Designed such disclosure controls and procedures, or caused such
            disclosure controls and procedures to be designed under our
            supervision, to ensure that material information relating to the
            Company, including its consolidated subsidiaries, is made known to
            us by others within those entities, particularly during the period
            in which this annual report is being prepared;

      (b)   Evaluated the effectiveness of the Company's disclosure controls and
            procedures and presented in this annual report our conclusions about
            the effectiveness of the disclosure controls and procedures, as of
            the end of the period covered by this annual report based on such
            evaluation; and

      (c)   Disclosed in this annual report any change in the Company's internal
            control over financial reporting that occurred during the period
            covered by this annual report that has materially affected, or is
            reasonably likely to materially affect, the Company's internal
            control over financial reporting.

5.    The Company's other certifying officer and I have disclosed, based on our
      most recent evaluation, to the Company's auditors and the audit committee
      of the Company's board of directors (or persons performing the equivalent
      function):

      (a)   All significant deficiencies and material weaknesses in the design
            or operation of internal controls over financial reporting, which
            are reasonably likely to adversely affect the 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 who have a significant role in the Company's
            internal controls over financial reporting.

Date: June 28, 2004

                                        By:       /s/ Chi Wen Tsai
                                               ---------------------------------
                                        Name:  Chi Wen Tsai
                                        Title: Chief Executive Officer