[SCHEDULE TO/A (RULE 14d-100) Tender Offer Statement SILICONWARE PRECISION INDUSTRIES CO., LTD. (Name of Subject Company (Issuer)) ADVANCED SEMICONDUCTOR ENGINEERING, INC. (Offeror) American Depositary Shares, Each Representing Five Common Shares, (Title of Class of Securities) 827084864 (American Depositary Shares) (CUSIP Number of Class of Securities) TW0002325008 (Common Shares) (ISIN Number of Class of Securities) Joseph Tung (Name, Address and Telephone] [Condition"). In addition, the U.S. Offer is subject to the conditions set forth in "The Offer—Section 14—Conditions to the U.S. Offer". This U.S. Offer to Purchase and the related ADS Letter of Transmittal and Common Share Form of Acceptance contain important information, and you should carefully read both in their entirety before making a decision with respect to the U.S.] [QuickLinks -- Click here to rapidly navigate through this document AMENDED AND RESTATED ADS LETTER OF TRANSMITTAL To Tender American Depositary Shares of by THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 1:30 A.M., NEW YORK CITY TIME, ON SEPTEMBER 22, 2015, UNLESS THE U.S. OFFER IS EXTENDED NO GUARANTEED DELIVERY Please deliver this properly completed and duly executed] [QuickLinks -- Click here to rapidly navigate through this document COMMON SHARE FORM OF ACCEPTANCE To Tender Common Shares of Siliconware Precision Industries Co., Ltd. by Advanced Semiconductor Engineering, Inc. THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 1:30 A.M., NEW YORK CITY TIME, ON SEPTEMBER 22, 2015, UNLESS THE U.S. OFFER IS EXTENDED NO GUARANTEED DELIVERY Please deliver] [QuickLinks -- Click here to rapidly navigate through this document of for by THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 1:30 A.M., NEW YORK CITY TIME, ON SEPTEMBER 22, 2015, UNLESS THE U.S. OFFER IS EXTENDED Please note that The Depository Trust Company and its participants, including the custodians for Euroclear and Clearstream, will establish their own cut-off] [QuickLinks -- Click here to rapidly navigate through this document Amended and Restated U.S. Offer to Purchase for Cash Outstanding American Depositary Shares and of Siliconware Precision Industries Co., Ltd. for NT$225.00 Per American Depositary Share (Payable in U.S. Dollars) and by Advanced Semiconductor Engineering, Inc. THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 1:30 A.M., NEW YORK CITY] [QuickLinks -- Click here to rapidly navigate through this document Amended and Restated U.S. Offer to Purchase for Cash of Siliconware Precision Industries Co., Ltd. for NT$225.00 Per American Depositary Share (Payable in U.S. Dollars) and by Advanced Semiconductor Engineering, Inc. THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 1:30 A.M., NEW YORK CITY TIME, ON SEPTEMBER 22, 2015,] [QuickLinks -- Click here to rapidly navigate through this document Amended and Restated U.S. Offer to Purchase for Cash of Siliconware Precision Industries Co., Ltd. for NT$225.00 Per American Depositary Share (Payable in U.S. Dollars) and by Advanced Semiconductor Engineering, Inc. THE U.S. OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 1:30 A.M., NEW YORK CITY TIME, ON SEPTEMBER 22, 2015,]