London — 

On Tuesday, investors were dumping AI stocks, worried that frothy valuations may be running away from reality. By Thursday, they were believers again.

Micron Technology (MU), a US chipmaker, posted blockbuster quarterly results Wednesday afternoon, sending its stock up by more than 16% in pre-market trade Thursday.

The company reported a surge in profit during its third quarter to $28.2 billion – almost 15 times more than what it made during the same quarter a year ago. Revenues soared 346% over the same period.

Micron is a maker of memory semiconductor chips, a type of chip used by AI companies to run their models, which are in short supply globally. Micron said in its results that its customers had committed $22 billion to secure supplies of its chips.

It comes after Micron’s stock fell 13% on Tuesday, part of a global sell off of AI and AI-adjacent companies. The level of volatility is a testament to how much investors have riding on the industry – the slightest indication that companies may not deliver their promised returns can prompt a mass exodus from stocks.

The sell off didn’t appear to be triggered by anything specific. Some market analysts pointed to worries sparked by Google (GOOG) and SpaceX (SPCX) falling somewhat sharply the previous day while others suggested that investors had been spooked by likely forthcoming rate hikes by the Federal Reserve.

On Thursday, in the US, the tech-heavy Nasdaq and the S&P 500 were up 2.15% and 0.75% respectively in pre-market trade while the Dow was pointing up by 0.3%.

Europe’s benchmark Stoxx 600 index was up 0.6% by early afternoon local time. In Asia, Japan’s Nikkei 225 index closed up 4.6% while South Korea’s Kospi finished 5.4% higher. The latter tumbled 10% Tuesday, tripping a circuit breaker that prompted a 20-minute cooling off period.

On Tuesday, SK Hynix and Samsung, two of the world’s leading memory chipmakers, tumbled more than 12%, dragging the rest of South Korea’s stock market down with them (the two chipmaking giants make up about half of the Kospi’s total market value).

But SK Hynix’s stock shot up 13% on Thursday after the company disclosed plans for a listing on the US Nasdaq. SK Hynix, along with Micron, are members of the growing club of AI companies with $1 trillion-plus valuations.