The Nikkei 225 Index shed 1.6% to close at 51,117.26, extending a 1.1% drop on Wednesday. The broader Topix lost 0.8%.
The Nikkei gauge marked a record closing high on Tuesday, with gains over recent months driven largely by optimism over AI.
SoftBank Group, a major domestic investor in AI, and chip sector heavyweights like Advantest Corp and Tokyo Electron have been major beneficiaries of the trend.
“The decline in certain high-priced stocks, particularly AI and semiconductor-related stocks, is weighing heavily on the index today,” said Nomura Securities strategist Wataru Akiyama.
Shares in Japanese chemical manufacturers declined after China’s commerce ministry said it is launching an anti-dumping probe into imports of chemicals used in chipmaking.
The probe into imports of dichlorosilane from Japan comes amid strained ties between the two countries, with China this week banning exports of dual-use items to Japan. Shin-Etsu Chemical dipped 4%, while Mitsubishi Chemical eased 0.4%.
There were 74 advancers on the Nikkei against 149 decliners. SoftBank Group was the biggest percentage loser, sliding 7.6%, while Sumitomo Pharma was the sharpest gainer, rising 7.8%.