Exhibit 12.1
 CERTIFICATION OF OUR CHIEF EXECUTIVE OFFICER
  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 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 report;3.
    
    Based on my knowledge, the financial statements, and other financial
information included in this 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 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)) and internal
control over financial reporting (as defined in Exchange Act Rules
13a-15(f) and 15d-15(f)) 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 report is being prepared;(b)
    
    Designed such internal control over financial reporting, or caused
such internal control over financial reporting to be designed under
our supervision, to provide reasonable assurance regarding the
reliability of financial reporting and the preparation of financial
statements for external purposes in accordance with generally accepted
accounting principles;(c)
    
    Evaluated the effectiveness of the Companys disclosure controls and
procedures and presented in this report our conclusions about the
effectiveness of the disclosure controls and procedures, as of the end
of the period covered by this report based on such evaluation; and(d)
    
    Disclosed in this report any change in the Companys internal control
over financial reporting that occurred during the period covered by
this 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 of internal control over financial
reporting, 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.
  By:
    /s/ Chi-Wen TsaiName:
    Chi-Wen TsaiTitle:
    Chief Executive Officer