A theme fund's name describes a story, but its holdings describe something more measurable: how much of that fund already sits inside the S&P 500. Across the 388 thematic ETFs ETFIQ checked against their latest N-PORT filings, the typical fund holds 32% of its weight in stocks the S&P 500 already owns, and 72 of those 388 funds carry more than sixty percent of their weight in index names.
The theme-level numbers spread widely. Energy security and critical technology shows the highest median overlap with the S&P 500 at 85%, followed by AI infrastructure and chips at 63% and digital infrastructure and data centers at 62%. At the other end, cannabis funds show 0% overlap with the S&P 500, and silver miners sit at 2%. Gold miners, coal, copper, rare earth and critical materials, and lithium and battery metals all show overlap in the single digits. Active share, the measure of how different a portfolio is from the index by weight, mirrors this: gold miners, silver miners, nuclear and uranium, water, and several metals and mining themes post active share of 100%, while energy security and critical technology, at 95%, and semiconductors, at 85%, sit lower.
Fees do not track this overlap in any simple way across the full set. The median fee across 415 funds and 54 themes is 0.60%, and when ETFIQ measures the fee against only the portion of each portfolio that differs from the S&P 500, the median fee for that difference is also 0.60%. Within individual themes the two numbers sometimes diverge: artificial intelligence funds charge a median 0.70% overall but 0.80% measured against the non-index portion, while cannabis funds charge 0.80% overall but 0.60% against the difference.
Overlap between funds, not just between a fund and the index, also appears in the data. ETFIQ found 127 pairs of funds across all themes whose portfolios are more than half identical by weight. The listed examples include GII and IGF in infrastructure, which overlap by 97%, IBB and IBBQ in biotech at 86%, and AUAU and GDX in gold miners at 84%. Several semiconductor pairs also appear with high overlap, including SOXQ and SOXX at 83% and FTXL and SOXX at 78%. Fees on these overlapping pairs vary: IBB charges 0.44% against IBBQ's 0.19%, while SOXQ charges 0.19% against SOXX's 0.33%.
One-year returns, measured against the S&P 500, split along similar lines. Semiconductors funds beat the S&P 500 in 9 of 9 cases with a median total return of +68.8%, and biotech did so in all 8 of its funds, returning +39.0%. Defense, infrastructure, internet and e-commerce, nuclear and uranium, clean energy, blockchain and crypto equities, and electric vehicles and batteries each show 0 funds beating the S&P 500 over the same period, with median returns ranging from +8.2% for infrastructure down to −31.9% for blockchain and crypto equities.
Readers can look up any individual fund's in-index weight, active share, fee, and one-year return, along with its closest-overlapping peer fund, on ETFIQ's fund pages.