The U.S. stock market is becoming increasingly dependent on three mega-cap technology companies — Nvidia Corp. (NASDAQ:NVDA), Apple Inc. (NASDAQ:AAPL) and Microsoft Corp. (NASDAQ:MSFT).

The trio now accounts for more than 21% of the S&P 500, according to Creative Planning data cited by Yahoo Finance, marking the highest concentration in just three stocks in the benchmark’s history. By comparison, IBM (NYSE:IBM), AT&T Inc (NYSE:T) and ExxonMobil Holdings Corp (NYSE:XOM) together represented 13.4% of the S&P 500 at their peak in the mid-1980s.

That concentration matters for ETF investors because the largest S&P 500 funds are market-cap weighted, meaning the biggest companies receive the largest allocations.

SPY, VOO Investors Have Significant Mega-Cap Exposure

The SPDR S&P 500 ETF Trust (NYSE:SPY) has Nvidia at 8.63%, Apple at 7.25% and Microsoft at 5.82%. Together, the three accounted for roughly 21.7% of SPY.

The Vanguard S&P 500 ETF (NYSE:VOO) showed a similar concentration, with Nvidia at 8.08%, Apple at 7.03% and Microsoft at 5.69%. That puts the combined exposure at about 20.8%.

This means investors buying broad-market ETFs are getting substantial exposure to the performance of just three companies, even though the funds hold hundreds of stocks.

QQQ Takes the Concentration A Step Further

The concentration is even more pronounced in the Invesco QQQ Trust (NASDAQ:QQQ), which tracks the Nasdaq-100.

Nvidia represents 8.53% of QQQ, Apple 7.2% and Microsoft 5.78%. Combined, the three accounted for roughly 21.5% of the ETF.

The distinction is important: while QQQ offers exposure to 100 companies, its portfolio remains heavily tilted toward the largest technology and growth names.

For investors looking to reduce this mega-cap concentration, the Invesco S&P 500 Equal Weight ETF (NYSE:RSP) takes a different approach, assigning roughly equal weights across S&P 500 constituents rather than allowing the largest companies to dominate the portfolio. RSP had 508 holdings.

With Nvidia, Apple and Microsoft driving a record share of the S&P 500, the growing question for ETF investors is no longer simply whether they own the broader market — but how much of that market is effectively riding on three stocks.

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