TAIPEI, March 8 (Reuters) - A senior executive of the Taiwan operation of Credit Suisse Group is under investigation for suspected insider trading, a Taiwan prosecutor said on Wednesday.

Elsa Chiu is suspected of illegal trading related to the June purchase of local firm Hermes Microvision Inc by the Netherlands' ASML Holding NV ASML.AS , for which Credit Suisse acted as advisor, Taipei District Prosecutors Office spokesman Chang Chieh-Chin told Reuters.

"During the merger and acquisition activities, there were some trading irregularities, and the stock exchange regulator detected this irregular trading," said Chang, who is also a deputy chief prosecutor.

Credit Suisse AG CSGN.S declined to provide immediate comment.

Chang said Chiu was questioned over Tuesday and Wednesday and that she posted bail of T$5 million ($162,059). He said her husband was also suspected of involvement and posted bail of T$6 million. Neither have been charged or arrested.

In Taiwan, suspects can be summoned to assist with investigations and can be requested to post bail before release.

Neither Chiu nor her husband could be immediately reached for comment.

Chiu is in charge of investment banking at Credit Suisse in Taiwan.

Several other individuals "who have relationships with the couple" are also under investigation, Chang said.

Speaking with reporters on the sidelines of parliament on Wednesday, Lee Ruey-Tsang, chairman of the Financial Supervisory Commission, confirmed the ASML-Hermes Microvision deal was being investigated, but declined to elaborate.

Dutch chipmaking equipment firm ASML bought industry peer Hermes Microvision for around T$100 billion. urn:newsml:reuters.com:*:nL1N19802W ($1 = 30.8530 Taiwan dollars)

(Reporting by Jess Macy Yu and J.R. Wu; Additional reporting by Emily Chan and Michelle Price; Editing by Christopher Cushing and Alexander Smith) ((JessicaMacy.Yu@thomsonreuters.com; +886 2500-4882 x501;))