SoftBank Group shares jumped 16.5% on Wednesday. Buying flooded into Japanese tech stocks, and the Nikkei 225 hit a record high.

CNBC reported on Wednesday local time that Japanese stocks, reopening after holidays, priced in the global artificial intelligence rally in one move. Semiconductor and AI-related shares led the gains.

The rise was not limited to SoftBank alone. Chip testing equipment maker Advantest rose about 7.8%, while semiconductor equipment maker Tokyo Electron gained 9.2%. Renesas Electronics also surged 13.8%. If SoftBank holds its gains, it will mark its biggest one-day rise since 2020.

Behind the move was an AI-led rally in U.S. stocks. Overnight, the Nasdaq Composite again set a record high, and U.S. AI-related shares also jumped. AMD rose 18.6%, Arm Holdings gained 13% and Super Micro Computer climbed 24.5%.

Japan’s market was closed in the latter part of Golden Week, and it is seen as having priced in the global rise in risk assets all at once when trading resumed.

Billy Leung (빌리 렁), an investment strategist at Global X ETFs, said global risk assets surged while Japan’s market was closed. He explained that the Nikkei’s move was effectively like reflecting three trading days of fluctuations in a single day.

He said that while the Tokyo market was closed, both the S&P 500 and the Nasdaq set fresh highs and semiconductor and AI shares led the gains. He then singled out Advantest and Tokyo Electron as the stocks that best reflect the AI semiconductor trend in Japan’s stock market.

Arm and OpenAI links were cited as a key reason SoftBank’s gain was particularly large. Leung explained that SoftBank effectively serves as a listed proxy for OpenAI and Arm. That means the market is reflecting expectations for expanded AI infrastructure through SoftBank.

Signs of easing geopolitical tensions also lifted investor sentiment. As signals emerged that tensions between the United States and Iran could ease somewhat, oil prices fell, which strengthened overall risk-on sentiment.

Some in the market say the strength in Japanese tech stocks reflects a combination of expectations for expanded AI infrastructure and rising U.S. semiconductor shares, rather than short-term supply and demand. In particular, as the view linking SoftBank, Arm and OpenAI has strengthened, funds continue to concentrate in AI bellwether stocks within Japan’s stock market.