Jim Cramer says this old-school investing concept still wins — even in the AI boom

CNBC's Jim Cramer on Tuesday emphasized the importance of diversifying beyond the market's hottest artificial intelligence winners.

"I don't want you getting blown out because you owned nothing but semis and the group has a bad day," the "Mad Money" host said, referencing how investing with borrowed money can heighten the consequences of hot stocks cooling off.

Many stocks tied to AI infrastructure and data centers have posted extraordinary gains over the past year, particularly memory-chip makers like Micron and Western Digital. However, recent pullbacks across that cohort have highlighted how quickly momentum can reverse. While Cramer said he remains bullish on the long-term outlook for the AI trade, he warned that no single investment theme should dominate a portfolio.

"I'm not anti-tech. But I do like diversification," he said.

Cramer pointed to the investors who lost fortunes by concentrating their portfolios in internet stocks during the dot-com bubble and financial institutions ahead of the Great Recession. He said he witnessed firsthand how quickly leveraged bets on a single sector could wipe out even sophisticated investors.

"I've seen so many people never ever come back" from owning stocks that went to zero during the dot-com crash, Cramer said.

Rather than abandoning technology altogether, Cramer said investors should broaden their exposure by owning high-quality companies benefiting from different long-term trends.

He highlighted Johnson & Johnson for its innovative drug pipeline and 3M for its renewed focus on innovation across a variety of industries. Cramer also pointed to CVS Health's combination of retail pharmacies and health insurance, as well as financial firms such as Goldman Sachs, Wells Fargo and BNY, arguing they offer compelling growth opportunities at valuations well below many AI leaders. Cramer's Charitable Trust, the portfolio run by CNBC's Investing Club, owns shares of Johnson & Johnson, Goldman Sachs and Wells Fargo.

"It just doesn't make sense to me why you can't diversify into these other stocks and make money, something we do with my Charitable Trust, where we've given out almost $5 million in gains by being diversified through thick and thin for 25 years," Cramer said.