Thematic ETFs are often sold as a way to get targeted exposure to a trend that sits outside the mainstream market. The data as of 2026-10-12 shows that, for most of these funds, a meaningful share of that exposure is already available in the S&P 500. Across 391 funds, the typical thematic ETF holds 32% of its weight in stocks the S&P 500 already owns, and 74 of those funds have more than sixty percent of their weight in index names.
How much a fund overlaps with the index varies widely by theme. Energy security and critical technology funds have a median 85% of weight in S&P 500 names, and AI infrastructure and chips funds sit at 65%, as do semiconductors at 64% and digital infrastructure and data centers at 62%. At the other end, cannabis funds show 0% overlap, gold miners 5%, silver miners 2%, and nuclear and uranium 16%. Active share, the flip side of this measure, tracks accordingly: gold miners, silver miners, nuclear and uranium, and several metals and mining themes show active share at or near 100%, while energy security and critical technology sits lower at 95% and semiconductors at 85%.
Fees do not appear to adjust for this. Across 54 themes and 419 funds, the median fee is 0.60%, and when fees are measured only against the part of each fund's portfolio that differs from the S&P 500, the median fee for that difference is also 0.60%. In other words, the price charged for the distinctive part of a thematic fund's holdings is, on a median basis, no different from the price charged for the whole fund. Some themes show a small gap between the two numbers, such as artificial intelligence at 0.70% fee against 0.80% fee for the difference, or robotics and automation at 0.80% against 0.80%, while cannabis shows 0.80% fee against 0.60% for the difference.
Overlap is not confined to comparisons with the S&P 500. Looking across fund pairs within the same themes, 130 pairs hold portfolios that are more than half identical by weight. The closest matches include GII and IGF in infrastructure at 97% weight overlap, IBB and IBBQ in biotech at 86%, and MARS and ORBX in space at 84%. Several semiconductor pairs also show overlap above 70%, including SOXQ and SOXX at 83% and FTXL and SOXX at 78%. In cases like these, holding both funds in a pair is close to holding one of them twice, though the fees attached to each side of a pair can differ, as with IBB at 0.44% and IBBQ at 0.19%.
Returns over one year varied by theme without a consistent relationship to overlap level. Semiconductors returned 91.7% with 9 of 9 funds beating the S&P 500, while defense returned −5.0% with 0 of 14 funds beating it, and both infrastructure and nuclear and uranium also showed no funds beating the index over one year, at +7.8% and −24.0% respectively.
Readers can look up any individual fund's in-index weight, active share, fee, and fee for the difference, along with its one-year return and whether it beat the S&P 500, on ETFIQ's fund pages.