Taiwan is investigating the alleged theft by two former executives of sensitive technology from leading flat-panel maker AU Optronics and its sale to a Chinese rival, officials said Monday.

The two suspects, identified by their surnames Lien and Wang, were taken into custody and questioned by the Bureau of Investigation last month.

The bureau said it suspected they had stolen AMOLED (active-matrix organic light-emitting diode) display technology used in mobile devices and televisions, before being recruited by China Star Optoelectronics Technology, a unit of China's consumer electronics brandname TCL.

"They were paid in return a yearly salary of more than $1 million," the bureau said in a statement.

"The illegal leak of the cutting-edge technology has undermined Taiwan's competitive edge in the flat-panel industry and severely betrayed the national interest."

The pair were released after questioning, the bureau said, but will face further questioning by prosecutors.

Lien had been in charge of AU Optronics' display technology development centre and Wang was a research unit manager before they moved to China Star in September last year.

The case comes amid mounting calls for a law on industrial espionage, especially by China, as growing ties have made it easier for mainland firms to steal secrets.

Currently suspects faces charges such as breach of trust and embezzlement but critics say the punishment for such crimes is not severe enough.

Taiwan Semiconductor Manufacturing Co filed a lawsuit against its Chinese rival Semiconductor Manufacturing International Corp in the United States in 2003, alleging SMIC improperly obtained its trade secrets and infringed patents.

In 2005 SMIC agreed to pay TSMC $175 million to settle the case after the Taiwan chipmaker filed new evidence of corporate espionage with a US court.