“There was excitement about A.I., and Nvidia ratified that excitement with blowout earnings,” Siegel said on CNBC on Monday. 

Shares in Nvidia surged by over 24% on Thursday after the chipmaker surprised analysts by forecasting $11 billion in sales for the current quarter, much higher than expected. The jump in share prices increased Nvidia’s market capitalization by $184 billion. And it was more than just Nvidia: A.I. stocks added $300 billion in value on Thursday, according to Reuters, as investors plunged into companies working on the new technology.

By market close Friday, Nvidia’s market cap had risen to over $960 billion, bringing it close to the $1 trillion threshold now held by just four U.S. companies: Apple, Microsoft, Alphabet, and Amazon. 

While admitting that A.I.-related stocks may be “slightly overvalued” in the long term, Siegel noted that in the short term “momentum can carry stocks far higher than their fundamental value, and no one can predict how high they might go.”

The A.I.-fueled boom is “not a bubble yet,” he said. 

He contrasted Nvidia’s jump in share price to earlier bubbles, like the dotcom bubble. During the late ’90s, “we were getting tremendous valuations from companies that had no earnings,” he said, unlike Nvidia, which he characterized as a “real, good company.”

Nvidia reported a record $4.58 billion in revenue from its data center business last quarter, a record high for the division that’s closely connected to the growth in generative A.I. and machine learning. The company reported $7.1 billion in total revenue for the quarter.

Companies are seeking to upgrade a trillion dollars’ worth in data center infrastructure, CEO Jensen Huang said on a call with analysts Wednesday. 

A.I.-rally doubts

Not everyone is convinced. Economist David Rosenberg told CNBC on Thursday that the boom in A.I. stocks “looks very weird” and is “way overextended.”

“No question we have a price bubble,” he said on Thursday. 

A model from David Trainer, founder of investment research firm New Constructs, suggests that Nvidia would need to increase revenues by 20% annually for 20 years to reward its investors. “This is priced for fantasy,” Trainer told Fortune after Nvidia’s jump in value.

Nvidia continues to double down on A.I. The company announced a suite of new A.I.-powered services on Monday at Taiwan’s Computex conference. The chipmaker announced a new supercomputer platform that would help tech companies like Microsoft and Meta create the next ChatGPT, as well as a new partnership with WPP to use generative A.I. to create new advertising. 

“I know it’s too much,” Huang said at the end of his keynote address.