SoftBank Stock Surges 18% as Markets Reopen, Fueled by AI Tailwinds and New Japan Server Project

SoftBank shares jump 18.44% in biggest gain since 2020, driven by AI server production talks with Nvidia and Foxconn, strong Arm earnings, and OpenAI investment.

SoftBank shares exploded higher on Thursday, recording their biggest single-day gain since 2020 as Japanese markets reopened after an extended Golden Week holiday. The stock jumped 18.44% to hit the daily limit of 6,424 yen, with more than 84 million shares changing hands — an extraordinary volume for a single session.

The rally was a catch-up move. While Tokyo was closed for the holiday period, the S&P 500 and Nasdaq both powered to fresh all-time highs. The Nikkei 225 itself surged 5.91% to 63,030 points, but SoftBank led the charge. "Japan was closed during Golden Week while global risk assets exploded," said Billy Leung, investment strategist at Global X ETFs. "Today's move is the Nikkei compressing three sessions into one."

A New AI Infrastructure Play in Japan

Adding rocket fuel to the rebound, reports emerged that SoftBank Corp is in talks with Nvidia and Foxconn to establish production of AI servers in Japan. The plan envisions initially assembling external components before eventually bringing full manufacturing in-house. The servers would run high-performance graphics processors at speed, targeting the growing demand for so-called "sovereign AI" — computing infrastructure produced within a country's own borders.

The project is expected to be included in SoftBank's medium-term management plan, with an official announcement potentially coming as early as Monday.

Arm and OpenAI: The Engines Under the Hood

SoftBank's surge wasn't just about catching up to global markets. The company's British chip subsidiary Arm Holdings reported unexpectedly strong quarterly earnings late Wednesday, citing unrelenting demand for high-performance chips used in AI data centers. SoftBank owns roughly 90% of the chip designer, and Arm's rising valuation flows directly into its parent's balance sheet.

The Japanese conglomerate has also deepened its ties with OpenAI, committing an estimated $64.6 billion to the AI pioneer for a roughly 13% stake. "SoftBank is effectively the publicly traded vehicle for OpenAI and Arm," Leung noted. The EU Commission gave the relationship a further boost on Tuesday, formally approving a joint venture between SoftBank and OpenAI without raising competition concerns.

In the October-December quarter, SoftBank posted a net profit of 248.6 billion yen, driven largely by valuation gains from its OpenAI investment. Arm shares had already climbed sharply on Wall Street before Tokyo even opened.

The Debt Side of the Equation

The blistering performance comes with a clear warning. SoftBank sold its Nvidia stake and portions of its T-Mobile holdings, while taking on more debt secured against its telecommunications subsidiary. The loan-to-value ratio has climbed from 16.5% three months ago to 20.6% — a level that leaves little room for error if markets turn.

The company's debt-to-equity ratio stands at 1.63, and its interest coverage ratio is just 0.83. As long as markets reward risk-taking, the structure holds. But a reversal would expose the fragility of the setup. "SoftBank is extremely sensitive to potential valuation declines in its core holdings," one market observer noted.

The broader Japanese tech sector joined the rally, with semiconductor names like Kioxia and Ibiden also posting double-digit gains after missing the global upswing during the holiday week.

What Comes Next

SoftBank is scheduled to report full quarterly results on May 13, with a presentation of the management plan expected on Monday. That will provide the next major test of the company's AI ambitions. Meanwhile, the complete consolidated earnings report due at the end of May will offer concrete data on how the radical pivot toward AI infrastructure is translating into operating performance.

For now, investors are betting that SoftBank's dual exposure — through Arm on the chip side and OpenAI on the software side — positions it as one of the purest plays on the artificial intelligence boom available in public markets. The question is whether the debt-fueled strategy can withstand the inevitable volatility that comes with such high-stakes wagers.