A theme fund's pitch is usually built on what it excludes as much as what it holds. The data suggest that promise varies widely by category. Across 379 funds, the typical thematic ETF carries 29% of its weight in stocks the S&P 500 already holds, and 74 of those funds are more than sixty percent overlapped with the index. That leaves a wide middle ground between funds that look almost nothing like the S&P 500 and funds where a majority of the portfolio duplicates it.
By theme, the range runs from near-total separation to heavy overlap. Cannabis and coal show 0% median weight in the S&P 500, and several metals and mining themes, including silver miners at 2%, gold miners at 5%, and copper at 10%, sit in similar territory. At the other end, Energy security and critical technology has an 86% median in-index weight, and Semiconductors, AI infrastructure and chips, and Digital infrastructure and data centers each carry more than 60%. Active share, the share of a fund's weight that differs from the S&P 500, moves in the opposite direction: themes with low index overlap tend to show active share near or at 100%, while Semiconductors, Metaverse and immersive tech, and AI infrastructure and chips show lower numbers, in the 77% to 88% range.
Fees do not track this pattern closely. Across 405 funds and 54 themes, the median fee is 0.60%, and when that fee is measured only against the part of each fund that differs from the S&P 500, the median fee for the difference is also 0.60%. Some themes charge the same either way, including Gold miners, Defense, and Copper. Others show a gap: Artificial intelligence moves from 0.70% to 0.80%, Broad innovation and megatrends from 0.50% to 0.60%, and AI infrastructure and chips from 0.70% to 0.80%, meaning the fee attached to the non-index portion runs higher once the S&P 500 overlap is set aside.
One-year returns and index overlap show no fixed relationship in the table. Semiconductors, with 66% in the S&P 500, beat the S&P 500 in 9 of 9 funds and posted a median total return of +100.4%. Gold miners, with only 5% overlap, also beat it in 9 of 9 funds, returning +36.3%. Defense, at 39% overlap, beat the S&P 500 in 0 of 14 funds. The record-versus-benchmark count varies by theme regardless of how much index weight each fund carries.
The second table turns to overlap between funds rather than between a fund and the index. It lists 139 pairs of funds whose portfolios are more than half identical by weight, of which 15 appear here, led by EVMT and PDBA at 97% weight overlap in Electric vehicles and batteries, and SOXQ and SOXX at 86% in Semiconductors. Fees within these pairs sometimes diverge: SOXQ charges 0.19% against SOXX's 0.33%, and AUAU charges 0.35% against GDX's 0.51%, despite the shared holdings.
On the live desk, a reader can look up any single fund's current in-index weight, active share, and fee against its named pair or theme peers as of the latest filing date.