Advanced Semiconductor Engineering (ASE) will be able to continue raising its stake in Siliconware Precision Industries (SPIL) through open market purchases, Taiwan's Central News Agency (CNA) quoted market sources as saying in a recent report.

Ways for ASE to increase its stake in SPIL through open market purchases include intra-day trading, block trades, and acquisition of SPIL's Nasdaq-listed American depositary receipts (ADR), the report cited unspecified market sources as indicating.

If ASE's stake in SPIL exceeds the 33% threshold, ASE will need to apply to Taiwan's Fair Trade Commission (FTC) to merge with SPIL, the report said.

ASE was able to complete its most-recent acquisition of additional SPIL shares through open market purchases, thanks mainly to support from financial institutions and investment funds, the report noted.

ASE on March 24 issued a company filing with the Taiwan Stock Exchange (TSE) disclosing the company had acquired 15,218,365 SPIL shares at a price of NT$51.56 (US$1.58), or a total of about NT$784.7 million. The acquisition boosted ASE's stake in SPIL to 25.49%, according to the filing.

Taiwan's FTC recently announced the authority had decided to terminate its review of an application submitted by ASE to acquire additional SPIL shares through a tender offer, as the tender offer already expired and would not be extended. ASE has responded arguing the decision is "completely without legal basis and violates the FTC's own administrative precedents." ASE added the company "will continue with our plan to acquire 100% equity interest in SPIL through all legally permissible means and avenues."