The Vanguard S&P 500 ETF (VOO) Is Unstoppable -- but There's a Quiet Risk Many Investors Are Overlooking

The Vanguard S&P 500 ETF (NYSEMKT: VOO) recently made stock market history by becoming the first exchange-traded fund (ETF) to surpass $1 trillion in assets.

It's no surprise that this fund is the most popular ETF among investors, as the S&P 500 ETF is a powerhouse of an investment and a core holding in millions of portfolios.

However, the S&P 500 (SNPINDEX: ^GSPC) has been quietly changing over the past couple of decades, and it may not offer the same level of stability that made it so popular.

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A tech-heavy behemoth

The S&P 500 is a market-cap-weighted index, meaning larger companies account for a greater share of total assets. In theory, this is a good thing. Bigger organizations tend to be healthier and more robust, offering extra stability to this investment.

But with the tech industry experiencing staggering growth in the past several years, much of the index is now controlled by just a handful of companies.

The "Magnificent Seven" -- which includes Nvidia, Apple, Microsoft, Amazon, Alphabet, Meta Platforms, and Tesla -- make up just over one-third of the S&P 500's value, as of June 2026. With mega-IPOs such as SpaceX, OpenAI, and Anthropic potentially joining the S&P 500 as soon as next year, the index could tilt even further toward big tech.

Again, this isn't always a bad thing. Tech stocks' seemingly unstoppable growth has lifted the S&P 500 to a long string of record highs, after all.

However, it also puts more risk-averse investors in a difficult place. The S&P 500 ETF is known for its stability and consistency, but its heavy emphasis on tech could result in more severe short-term volatility than some investors expect.

The right strategy is key right now

The Vanguard S&P 500 ETF can still be a smart buy right now, but it's wise to take a couple of extra precautions to protect your portfolio:

• Keep a long-term outlook: Tech stocks can be volatile in the short term, but many deliver lucrative returns over time. The S&P 500 ETF may experience more severe price swings thanks to its tech tilt, so it's wise to prepare to hold this investment for at least five years to help reduce the impact of that volatility.
• Focus on diversification: Because the S&P 500 leans toward large-cap tech, it can be helpful to balance your portfolio with stocks from other corners of the market, such as small-cap stocks, value stocks, or dividend stocks. The more well-rounded your portfolio, the more protected you'll be against turbulence.

With the right strategy, this investment can still be lucrative. If you'd invested $5,000 in the Vanguard S&P 500 ETF 10 years ago, for example, you'd have more than $21,500 by today. Just be sure you're aware of the increased potential for short-term volatility if you choose to invest.

Katie Brockman has positions in Vanguard S&P 500 ETF. The Motley Fool has positions in and recommends Alphabet, Amazon, Apple, Meta Platforms, Microsoft, Nvidia, Tesla, and Vanguard S&P 500 ETF. The Motley Fool has a disclosure policy.