Shares of Taiwan Semiconductor Manufacturing Company surged on Tuesday after Warren Buffett’s Berkshire Hathaway disclosed that it had purchased a $4.1 billion stake in one of the world’s largest chipmakers.

In a filing with the United States’ Securities and Exchange Commission on Monday, Berkshire Hathaway (BRKA) said it acquired about 60 million American depository shares of TSMC (TSM) in the three months ended September.

Shares of TSMC were up over 8% in Taiwan on Tuesday.

“TSMC welcomes all investors with the propensity to buy and hold TSMC’s stock,” a spokesperson for the chipmaker said.

TSMC accounts for an estimated 90% of the world’s super-advanced computer chips, supplying tech giants including Apple (AAPL) and Qualcomm (QCOM).

Berkshire’s purchase of a stake in the Taiwanese chip giant comes as tensions between China and the self-governed democratic island are escalating.

Taiwan has been facing growing military aggression from Beijing in recent months, and that has thrown a spotlight on the critical role it plays in the global chipmaking industry.

Super-advanced semiconductor chips — like the ones produced by TSMC — are difficult to make because of the high cost of development and the level of knowledge required, meaning much of the production is concentrated in just a handful of suppliers.

The firm — widely dubbed in Taiwan as its “sacred mountain” — is so important to the island that its employees can apply to be exempted from military reservist training, the defense ministry has said.

Tensions between Washington and Beijing have also been rising lately over chips, with President Joe Biden imposing a sweeping set of controls on the sale of advanced chips and chip-making equipment to Chinese firms. Experts fear that these controls could shift the tech arms race between the United States and China to a whole new level.

Berkshire also owns large stakes in Apple, Bank of America, Coca-Cola, Chevron, and American Express, CNN reports.