Recently, a friend asked me how the four major U.S. stock indices are categorized, which made me realize that many people actually don’t understand the differences and purposes of these indices. So I decided to organize this information, hoping it will help those interested in entering the U.S. stock market.

First, let’s start with the conclusion: because there are so many listed companies in the U.S., unlike Taiwan’s stock market which only has the Weighted Index, there are multiple indices each representing different aspects of the market. The four most important are the Dow Jones Industrial Average, S&P 500, Nasdaq, and the Philadelphia Semiconductor Index, each with its own characteristics.

The Dow Jones Industrial Average is the oldest, established in 1896. It currently includes 30 companies and mainly reflects the performance of traditional economy and blue-chip stocks. Since it uses price weighting, companies with higher stock prices have more influence. This index is suitable for judging economic stability; when the market is uncertain, the Dow often outperforms Nasdaq in terms of resilience.

However, the problem with the Dow is that its sample size is too small to fully represent the entire U.S. stock market. That’s why the S&P 500 was created later, covering the top 500 companies by market capitalization in the U.S., accounting for about 75% of the total U.S. stock market value. The S&P 500 spans various industries and has strict selection criteria, only including companies with stable profits. Many people say it’s a barometer of the U.S. economy, and I think that’s quite accurate. If you want to grasp the long-term trend of the U.S. economy, looking at the S&P 500 is more reliable than the Dow.

Nasdaq is the dominion of tech stocks. Established in 1971, it was the first electronic stock exchange in the U.S. and has grown along with the tech industry, gradually becoming a global tech market indicator. Interestingly, Nasdaq’s movements are highly correlated with Taiwan’s stock market, which is why many Taiwanese investors pay close attention to it. Short-term traders often use Nasdaq as an immediate indicator of market sentiment—rising means funds are willing to take risks, while falling signals capital is starting to withdraw.

The Philadelphia Semiconductor Index is the youngest of the four, established in 1993, tracking 30 representative semiconductor companies. As demand for electronics, cloud computing, AI, and other tech sectors explodes, the market value of semiconductors has soared, making the Philly Semiconductor Index a global focus. With TSMC included in its components, the index’s fluctuations have a significant impact on Taiwan’s stock market. It’s a key indicator for tech stocks and Taiwanese investors.

What’s interesting is that these four indices sometimes show different trends. A common scenario is Nasdaq falling while the Dow rises, or vice versa. This usually indicates sector rotation—funds are shifting from overperforming tech stocks to undervalued traditional or defensive stocks. This doesn’t mean the market is crashing; it just shows funds are repositioning. So investors shouldn’t only watch the indices’ overall movement but also pay attention to which sectors are leading or lagging—the leading sectors reveal where the money is flowing. When all four indices move in the same direction, the trend’s reliability increases.

As for how to invest in these four major U.S. stock indices, there are three common methods. The first is ETFs, which are traded like regular stocks, usually with low management fees, but they don’t offer leverage and can only be bought long. The second is futures, which have expiry dates and leverage but require margin deposits, and since the U.S. stock market has no daily price limits, the risks are higher. The third is CFDs (Contract for Difference), allowing both long and short trading, with higher leverage, making them more suitable for short-term trading. The minimum investment is also relatively low—around $100.

For long-term investing, I recommend regularly buying ETFs that track the four indices—this is simple and convenient. If you want to profit from short-term price movements, then using futures or CFDs to leverage both long and short positions is the way to go. Regardless of the method, the key is to understand what each index represents so you can adjust your strategy flexibly based on market conditions.