A thematic ETF often promises exposure to a single idea, but the holdings do not always separate cleanly from the broad market. Across 390 funds with available data, the median fund holds 32% of its weight in stocks also found in the S&P 500. That share is far from uniform: 72 of the 390 funds carry more than 60% of their weight in S&P 500 names, meaning their returns are, by weight, mostly tied to companies already inside the mainstream index rather than to names unique to the theme.
The overlap varies widely by theme. Semiconductors shows a median of 66% of weight already in the S&P 500, with a median active share of 85%, while Energy security and critical technology sits even higher at 85% in-index weight. At the other end, Gold miners, Silver miners, Cannabis, and Coal show in-index medians at or near zero, with active share near 100%, meaning those portfolios differ almost entirely from the S&P 500's roster of holdings.
Fees do not track this distinction in a simple way. Across 415 funds and 54 themes, the median fee is 0.60%, and 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%. Theme by theme, some funds show the fee for the difference running higher than the headline fee: 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%. Others, like Cannabis, show the fee for the difference falling, from 0.80% to 0.60%. The gap between the two numbers gives a sense of how much of the stated fee is paying for exposure that is not already available through an S&P 500 fund.
A separate pattern shows up between funds themselves rather than against the index. Among all funds in the dataset, 126 pairs hold portfolios that are more than half identical to each other by weight. The closest pair is GII and IGF, both in Infrastructure, with 97% weight overlap and fees of 0.40% and 0.37%. Other close pairs include IBB and IBBQ in Biotech at 86% overlap, AUAU and GDX in Gold miners at 84%, and SOXQ and SOXX in Semiconductors at 83%. In several of these pairs, the fees charged differ even though the underlying holdings are largely the same, as with IBB at 0.44% against IBBQ at 0.19%.
Performance outcomes over one year also varied by theme, ranging from Semiconductors at a median total return of +58.0%, where 9 of 9 funds beat the S&P 500, to Blockchain and crypto equities at −34.1%, where 0 of 13 funds did. These numbers describe what happened over the one-year period measured and do not indicate what a theme, in-index share, or fee level will produce going forward.
Readers can look up any individual fund's in-index weight, active share, fee, and one-year return, along with its closest overlapping peers, on ETFIQ's fund pages.