Thematic exchange-traded funds are often sold as a way to get exposure that the broad market does not already provide. The data suggests that, by weight, much of what these funds hold is not new at all. Across 375 funds measured, the typical thematic ETF has 30% of its portfolio in stocks that the S&P 500 already holds. At 74 of those 375 funds, more than sixty percent of the portfolio by weight overlaps with S&P 500 names. The remainder of each fund's holdings, the part that differs from the S&P 500, is what ETFIQ calls active share, and across themes that number is typically high, often in the 90s or 100%.
The overlap varies widely by theme. Energy security and critical technology shows a median of 86% of weight already in the S&P 500, and AI infrastructure and chips, semiconductors, and digital infrastructure and data centers all sit above 60%. At the other end, gold miners, cannabis, lithium and battery metals, rare earth and critical materials, and silver miners show single-digit medians, meaning most of what these funds hold sits outside the S&P 500 altogether.
Fees do not appear to track this difference in a simple way. Across 405 funds and 54 themes, the median fee is 0.60%, and when fees are measured only against the part of each fund that differs from the S&P 500, the median fee for that difference is also 0.60%. In other words, restating the fee per unit of distinct exposure does not change the typical headline number. At the theme level, some funds show a lower fee on the distinct portion than on the whole fund, such as biotech (0.50% fee against 0.30% fee for the difference) and cannabis (0.80% against 0.60%). Others show the fee rising when measured against the distinct portion, such as artificial intelligence (0.70% against 0.80%) and AI infrastructure and chips (0.70% against 0.70%, unchanged) and timber and forestry (0.60% against 0.80%).
A separate pattern shows up among the funds themselves. Of the pairs examined, 129 pairs hold portfolios that are more than half identical by weight. The listed examples go further: PDBA and EVMT in agriculture share 99% of weight, AUAU and GDX in gold miners share 83%, and several semiconductor pairs, including SOXQ and SOXX, SHOC and SMH, and FTXL and SOXX, share between 74% and 82%. Fees within these pairs are not always matched. SOXQ carries a 0.19% fee against SOXX at 0.33%, and SPAM carries 0.35% against PSWD at 0.20%, despite holding largely the same stocks. Holding both funds in a pair is, by this measure, close to holding one of them twice.
One-year total returns differed sharply by theme, from semiconductors at +99.1% and genomics and gene editing at +84.0%, to defense at −2.5% and streaming and live entertainment at −23.6%. The data does not show whether these returns relate to the degree of S&P 500 overlap; themes with high overlap, like semiconductors, and themes with low overlap, like copper, both posted gains, while defense, with 39% overlap, posted a loss.
Readers using ETFIQ's live desk can check the current in-index weight, active share, and fee-for-difference numbers for any individual fund, not just the theme median shown here, and can look up whether two specific funds they hold appear among the overlapping pairs.