A look inside thematic ETFs shows that a meaningful share of their holdings are stocks already found in the S&P 500. Across 380 funds with the relevant data, the typical, or median, thematic fund has 30% of its weight in S&P 500 names. That leaves a median active share of 70%, meaning the remaining holdings sit outside the mainstream index. The overlap is not evenly spread: 74 of the 380 funds carry more than sixty percent of their weight in stocks the S&P 500 already holds.
The pattern varies widely by theme. Energy security and critical technology shows a median 86% of weight already in the S&P 500, alongside AI infrastructure and chips at 63% and Semiconductors at 62%. At the other end, Cannabis and Coal each show a median 0% in the S&P 500, and Silver miners sits at 2%. Gold miners, at 5%, and Nuclear and uranium, at 16%, also sit far from the mainstream index by this measure.
Fees tell a related story. Across 54 themes and 406 funds, the median fee is 0.60%. When the fee is measured only against the part of a fund that differs from the S&P 500, the median fee for that difference is also 0.60%, suggesting that, in aggregate, investors are not paying a markedly different rate for the distinct portion of these portfolios than for the whole. Within individual themes the two numbers sometimes diverge: Biotech shows a median fee of 0.50% against the whole fund but 0.30% for the difference, while Semiconductors shows 0.30% against the whole fund and 0.40% for the difference.
One-year total returns, measured against the S&P 500, ranged from +102.3% for Semiconductors (where 9 of 9 funds beat the index) to −14.8% for Nuclear and uranium (where 0 of 8 funds did). Defense funds returned +1.9% with 0 of 14 beating the S&P 500, while Internet and e-commerce returned −14.1% with 0 of 13 ahead of the index. Genomics and gene editing posted +90.6% with 3 of 3 funds ahead.
The data also point to overlap between individual funds, not just against the S&P 500. Among 406 funds, 136 pairs hold portfolios that are more than half identical by weight, meaning that for these pairs, holding both is close to holding one of them twice. The highest overlap recorded is 98%, between PDBA and EVMT in the Agriculture theme, both carrying a fee of 0.59%. Other close pairs include AUAU and GDX in Gold miners at 83% overlap, and SOXQ and SOXX in Semiconductors at 82% overlap.
Readers can check any fund's current in-index weight, active share, fee for the difference, and its listed overlap pairs on the live desk.