Thematic ETFs are often sold as a way to get exposure that the broad market does not already provide. The data as of 2026-10-02 shows a mixed picture on that front. Across 376 funds, the typical thematic ETF holds 30% of its weight in stocks already found in the S&P 500. At the high end, 74 of these 376 funds carry more than sixty percent of their weight in S&P 500 names, meaning the theme is, for the most part, already sitting inside a mainstream index fund.
The overlap varies widely by theme. Semiconductors funds show a median 62% of weight already in the S&P 500, and AI infrastructure and chips funds show 63%. Energy security and critical technology tops the list at 86%. At the other end, gold miners sit at a median 6% in the S&P 500, silver miners at 2%, and cannabis at 0%, meaning these themes hold almost nothing that a plain S&P 500 fund would already give an investor. Median active share, a measure of how much a fund's holdings differ from the S&P 500 by weight, runs as high as 100% for several metals and mining themes and as low as 80% for broad innovation and megatrends and for metaverse and immersive tech.
Fees add another layer. Across 406 funds in 54 themes, the median fee is 0.60%. When the fee is measured only against the part of each portfolio that differs from the S&P 500, the median is also 0.60%, since the overall median active share across funds is high enough that the two numbers land close together. Theme by theme, this distinction shows up more clearly. Semiconductors, for example, carries a median fee of 0.30% but a median fee of 0.40% once measured against only the non-overlapping portion of the portfolio, because part of what the fee is paying for is already available through index names.
Overlap is not limited to comparisons against the S&P 500. Within the thematic fund universe itself, 129 pairs of funds hold portfolios that are more than half identical to each other by weight. The closest pair, PDBA and EVMT in the agriculture theme, show a 99% weight overlap. Several semiconductor pairs, including SOXQ and SOXX at 82% and SHOC and SMH at 78%, also cluster near the top. In cases like these, holding both funds in a portfolio is close to holding one of them twice, though the two funds in a pair can still carry different fees, as with SOXQ and SOXX charging 0.19% and 0.33% respectively.
Fund counts and return patterns also vary by theme. Semiconductors, where nine of nine funds that could be measured beat the S&P 500 over one year with a median total return of +99.0%, sits in contrast to defense, where none of fourteen funds beat the S&P 500 despite a median return of −1.4%. These differences sit alongside, not in place of, the overlap and fee numbers above.
Readers working with a live desk can check any individual fund's current in-index weight, active share, and fee for the difference against the latest N-PORT filing data to see whether a specific theme still looks the way it does in this snapshot.