Advanced Semiconductor Engineering (ASE) has maintained that its plan to buy an additional 24.71% stake in SPIL through a tender offer will be carried out as scheduled.

"In order to protect the rights and interests of SPIL shareholders, ASE will lawfully commence the tender offer on December 29, 2015 as previously announced," ASE said in a statement.

SPIL said on December 28 its board of directors will agree to evaluate ASE's takeover proposal only if two conditions are met: termination of ASE's upcoming tender offer for more SPIL shares; and negotiations built on the basis of mutually agreed terms.

ASE on December 14 proposed to acquire all outstanding shares of SPIL, but failed to receive a positive response from SPIL. Later in the month, ASE disclosed it will launch an unsolicited tender offer for more SPIL common shares on December 29.

ASE currently holds a 25% stake in SPIL which was acquired through an unsolicited tender offer successfully executed in October.

"ASE sincerely hopes that the parties can commence negotiations on the (acquisition) proposal as soon as possible, and complete such negotiations before the expiration of the tender offer," ASE noted.

ASE's upcoming tender offer for more SPIL shares will expire on February 16, 2016.