04:15 PM EST, 11/20/2025 (MT Newswires) -- The Toronto Stock Exchange slumped again Thursday as investors remain jittery about big tech's huge artificial intelligence spending commitments, even after Nvidia (NVDA) posted strong results yesterday, and this is seen leading to a correction in technology valuations across North America.

The resources-heavy TSX closed down 371.86 points, or 1.2%, at 29,906.55, not helped by lower commodity prices and with most sectors lower. The index here was actually up over 300 points in early trade, but then swung nearly 700 points through the rest of the session as first AI fears resurfaced, and then took over market sentiment.

Among sectors, Base Metals was down 4% and Info Tech down 2.55%. But the Battey Metals Index did manage to achieve gains of 2.9%.

Veteran economist David Rosenberg said it has been many decades since one stock could move the market like Nvidia. Then again, he noted, it is a near-US$5 trillion mega cap that accounts for 8% of the S&P 500, and the company did indeed deliver across the top line, bottom line, and forward guidance after the bell yesterday. "The results kyboshed the malaise in the growth arena of the past several weeks," he added.

Still, Rosenberg said valuations "look excessive" even with strong AI Growth. He added: "This remains a bubble of epic proportions, keep that in mind, and while not in the same league as the late 1990s, a 38x P/E multiple for the Tech sector is about 60% above the two-decade average of 24x. Do the discounted cash flow assumptions really make sense even in the aftermath of Nvidia's results? Color me a skeptic that the total size of the AI market is going to swell eightfold in the next half-decade, which is what is currently being priced in."

Rosenberg noted the S&P 500 has become "concentrated like never before", with the top 10 companies comprising 40% of the total market capitalization. And, he noted, even within that group the concentration has really narrowed to a Mag Three; Nvidia, Microsoft, and Alphabet, the only three of the Magnificent Seven that have managed to outperform the index this year. "What was not resolved in Nvidia's results were all the issues still overhanging the rest of the Tech sector -- the circularity of the deals being announced, the debt binge, the strains on the energy grid, and the intensifying competition coming out of China," Rosenberg added.

Of commodities, gold prices eased Thursday even as the dollar and treasuries weakened as hopes for a December interest-rate cut from the Federal Reserve continue to fade. Gold for December delivery was down $16.30 to US$4,066.50 per ounce.

Also, West Texas Intermediate oil closed lower, a day ahead of the start of U.S. sanctions on Russia's two largest oil producers as rising supply offsets strong demand for refined products. WTI crude oil for December delivery closed down $0.30 to settle at US$59.14 per barrel, while January Brent oil was last seen down $0.23 to US$63.28.