Why is SoftBank Group stock tumbling today?

SoftBank Group Corp. stock plummeted by 8.0% to ¥5,337 on Tuesday, in sync with broader Asian tech share losses following a lengthy weekend, as the company's extensive and debt-financed ties to the artificial intelligence sector made it one of the most affected casualties on the Tokyo Stock Exchange. The immediate cause was a steep fall in U.S. semiconductor stocks that spread to regional markets, spurred by reports of a Chinese memory chipmaker making significant progress in high-performance chip development, raising concerns about heightened competition and possible price reductions in the global AI hardware supply chain.

SoftBank's substantial involvement in the AI sector — comprising approximately 87% stake in Arm Holdings and a combined $64.6 billion investment in OpenAI, representing around 13% ownership — renders the stock highly vulnerable to any alteration in AI sentiment. Furthermore, recent disclosures suggested that OpenAI's annualized revenue was closer to $50 billion, significantly lower than the approximately $70 billion previously speculated, leading investors to question whether the returns from SoftBank's concentrated position could sufficiently cover the high-yield debt utilized to finance it.

The company's credit default swaps had already risen to multi-year peaks in recent weeks, indicating that credit markets were growing increasingly concerned about the leverage embedded in SoftBank's AI strategy. The Nikkei 225 in Japan experienced a sharp decline on Tuesday, with the index dropping more than 1,900 points at one point due to the overwhelming impact of semiconductor-related stocks.

South Korea's KOSPI also suffered a significant decline, while the wider Asia-Pacific equity sector weakened in unison, as anticipation of crucial earnings from ASML and TSMC prompted caution towards technology.