Advanced Semiconductor Engineering (ASE) has proposed to acquire all outstanding shares of Siliconware Precision Industries (SPIL) for NT$55 (US$1.67) each. ASE currently holds a 25% stake in SPIL.

ASE's unsolicited offer came on the heels of SPIL's announcement that the company plans to sell 1.03 billion new shares to Tsinghua Unigroup at NT$55 - the same price that ASE has offered.

"The Tsinghua deal not only does not provide any cash to SPIL's shareholders, but will also significantly dilute the equity interests of SPIL's shareholders," ASE noted in a statement. "In contrast, our proposal is for an all cash offer that would provide immediate and certain cash value to SPIL's shareholders."

ASE will spend about US$4 billion to acquire SPIL's remaining stake, according to ASE CFO Joseph Tung. ASE expects to receive a reply from SPIL on its planned offer by December 21.

In response, SPIL said ASE's proposal will need to be discussed internally and the company currently has no feedback.

ASE indicated its investment in SPIL is "based on our sincere belief in the need for Taiwan's semiconductor packaging and testing industry players to actively seek opportunities for cooperation and resource consolidation to maintain and further improve the competitive strength of Taiwan's semiconductor packaging and testing industry in the face of intensified global competition and emerging competitors."