Nvidia stock accounts for more than a third of the S&P 500's gains this year—and it's a big risk for investors, top economist says

Jensen Huang speaks to reporters

Nvidia stock has continued its stunning rally this year, sending the AI chip leader's valuation past $3 trillion and making it an even bigger presence in the S&P 500.

In fact, 34.5% of the S&P 500's market cap gains so far this year can be attributed to Nvidia alone, according to Apollo Chief Economist Torsten Sløk.