TOKYO, Oct 29 (Reuters) - Japan's Nikkei share average

surged past the key 51,000 level for the first time on

Wednesday, underpinned by investor optimism over artificial

intelligence sector investments.

The tech-heavy Nikkei 225 Index was up 2.05% at an

unprecedented 51,249.82, as of the midday break. The index

crossed the key psychological barrier of 50,000 on Monday.

The broader Topix index edged up less than 0.1%, as

a stronger yen weighed on most non-tech shares.

Advantest ( ADTTF ), a key chip-testing equipment supplier to

major technology companies, soared more than 20% after the firm

hiked its annual profit forecast by one quarter on surging

demand.

"Stocks such as Advantest ( ADTTF ) and SoftBank Group are essentially

driving the stock market," said Nomura Securities strategist

Wataru Akiyama. "It's unclear how long this will last. Once the

initial wave passes, the upward momentum may ease."

All three major U.S. stock indexes closed at record highs

after AI darling Nvidia ( NVDA ) said it will build artificial

intelligence supercomputers for the U.S. energy department.

Shares of Microsoft ( MSFT ) jumped after the tech company

reached a deal that permits OpenAI to restructure into a public

benefit corporation while giving Microsoft ( MSFT ) a 27% stake in the

ChatGPT maker.

Japan's SoftBank Group, a major investor in chips

and AI, climbed 2.1% and was the second-biggest driver of the

Nikkei in terms of index points. Lasertec ( LSRCF ), another

semiconductor heavyweight, surged 7.8%.

There were 65 advancers in the Nikkei against 160 decliners.

The largest losers were Nidec ( NNDNF ), which lost another 7.3%

after being marked for exclusion in the Nikkei, followed by

SHIFT, down 5.3%.