His Berkshire Hathaway conglomerate has disclosed a $4.1 billion investment in Taiwan chipmaker TSMC.
The news sent shares in the firm soaring.
They closed nearly 8% higher on Tuesday (November 15).
TSMC stock had previously been battered by fears of a slowdown in demand for chips.
It all marks a relatively unusual move for Berkshire, which generally doesn't make big bets on tech.
It did put a lot of money into IBM over the last decade, but the move that didn't pay off.
However, it is sitting on huge unrealized gains from its big stake in Apple, which Buffett views more as a consumer goods company.
TSMC is the world's largest contract chipmaker, supplying the likes of Apple and Qualcomm.
Analysts says Buffett was probably attracted by its size and power in the sector.
Now 92 years old, he's run Berkshire since 1965.
The Omaha-based firm owns dozens of companies from the BNSF railroad to clothes maker Fruit of the Loom.
