TOKYO, June 1, 2026 (BSS/AFP) - Japan's tech investor SoftBank Group overtook Toyota on Monday to become the country's most valuable company, as the benchmark Nikkei index briefly reached a new high amid the AI boom.

SoftBank, a major backer of ChatGPT maker OpenAI, soared more than 11 percent in the afternoon trade, after its founder announced a 75-billion-euro ($87.5 billion) investment in AI infrastructure in France.

Masayoshi Son told La Tribune Dimanche weekly on Saturday that it "will be the largest investment in Europe in infrastructure related to artificial intelligence".

SoftBank said last month its annual net profit quadrupled to more than $30 billion, mainly thanks to its investment in OpenAI.

The company's market capitalisation swelled on Monday to more than 47 trillion yen, while that of Toyota fell to just under 46 trillion yen after its shares dropped nearly five percent.

The third largest is chipmaker Kioxia, formerly the semiconductor unit of engineering giant Toshiba. It jumped more than eight percent.

Global demand for the chips has been driven by the growth of AI technology.

The Nikkei index briefly surpassed 67,000 for the first time in the morning trade.