Comment on 5 trillion-dollar companies — including Nvidia, Apple, and Amazon — have been behind most of the S&P 500's 10% gains

New York Stock Exchange traders.Spencer Platt/Getty Images The S&P 500 index is on a tear, rising nearly 10% this year. But most of the gains are from a quintet of stocks that have surged massively this year. Alphabet, Amazon, Apple, Microsoft, and Nvidia are big winners this year. The S&P 500 index is on a tear, rising nearly 10% so far this year — in stark contrast to a 13% decline over the same period last year.But gains in the benchmark index — which tracks a broad range of sectors such as banks, manufacturing, tech, and retail — are thanks to massive upswings from just five companies: Apple, Microsoft, Alphabet, Amazon, and Nvidia, all of which have posted outsized gains in market cap this year so far.The companies are part of the elusive club of firms touching $1 trillion in market valuation, with Nvidia becoming the latest company to briefly hit the milestone before giving up some gains.Collectively, the five companies have raised their market cap by about $2.9 trillion in 2023 — contributing 96% of the almost $3 trillion gains in the S&P 500's market value this year, Fortune reported on Wednesday.This means the rest of the 495 companies in the S&P 500 contributed to just 4%, or $110 billion in the index's gain, per Fortune.The outsized gains of the five companies have also put the benchmark index under scrutiny for concentration risk, as Insider's Zahra Tayeb reported on Sunday.