NEW YORK, June 6 Reuters A rally that has propelled U.S. equities to record highs increasingly rests on redhot chipmaker Nvidia and a handful of other giant stocks, reviving concerns that the markets performance has become tied to a cluster of companies.

About 60 of the SP 500s total return of more than 12 for the year has been driven by five companies whose shares have some of the heaviest weightings in the index Nvidia, Microsoft, Meta Platforms, Alphabet and Amazon.com, data from SP Dow Jones Indices showed.

Nvidia which on Wednesday became the worlds secondmost valuable company following a 147 run this year has alone accounted for about a third of the indexs gain.

As the companies share prices have rallied, their weightings in the SP 500 have grown, giving them more sway over the broader index. The top four stocks Microsoft, Apple, Nvidia and Alphabet accounted for nearly 24 of the SP 500 at the end of May, the biggest collective weight for four stocks in 60 years, according to Bianco Research.

Many investors believe the companies market heft is deserved, given their robust earnings, dominant competitive positions and expectation they will capitalize on advances in the burgeoning artificialintelligence field. But some are concerned the concentration of gains in a handful of powerhouses could threaten indexes if some of the big names start to wobble.

If these names stop performing well … and we don39;t see the rest of the market providing that support, that…