(Bloomberg) -- The six biggest US companies now command a greater share of the S&P 500 Index than ever before.

Microsoft Corp., Apple Inc., Nvidia Corp., Alphabet Inc., Amazon.com Inc. and Meta Platforms Inc. account for 30% of the benchmark, up from about 26% at the start of the year, according to data compiled by Bloomberg. The S&P 500 is weighted by stocks’ market capitalizations. 

The uptick has been driven by Nvidia, which has rallied 20% since a bullish sales forecast last week showed that spending on artificial-intelligence computing remains strong. The chipmaker has added $1.6 trillion in market value this year and is close to overtaking Apple as the world’s second-most valuable company. 

Large companies have always dominated the S&P 500 but not to this extent. For most of the past three decades, the percentage weighting of the six biggest stocks in the benchmark was in the teens. It wasn’t until 2020 that the concentration exceeded 20%.

In another sign of a shift in the market, even at the height of the dot-com bubble in 2000, only three of the biggest six were technology companies — Microsoft, Cisco Systems Inc. and Intel Corp. The other three were General Electric Co., Exxon Mobil Corp. and Walmart Inc. 

--With assistance from Matt Turner.

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