A thematic ETF is often sold as a way to own a specific idea, from semiconductors to gold miners, separate from the broad market. The holdings data suggest the separation is partial. Across 392 funds, the typical thematic ETF holds 32% of its weight in stocks already in the S&P 500. In 73 of those funds, more than sixty percent of the portfolio by weight overlaps with the index. How much overlap exists varies sharply by theme. Energy security and critical technology shows a median of 85% of weight already in the S&P 500, and semiconductors and AI infrastructure and chips both show 65%. At the other end, cannabis, coal, silver miners and gold miners show medians of 0% to 5%, meaning those portfolios hold almost nothing that the S&P 500 already owns.
Active share, which measures how different a fund's weights are from the index, tends to run high even where in-index weight is also high. Semiconductors combines a 65% in-index number with an 85% active share, and AI infrastructure and chips pairs 65% with 87%. This happens because active share accounts for both which names are held and how heavily, so a fund can hold mostly familiar stocks while still weighting them very differently from the S&P 500.
Fees sit at a median of 0.60% across 54 themes and 419 funds. 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, the two numbers are close in most rows, for instance infrastructure shows 0.60% on both measures and clean energy shows 0.60% on both. In some themes the fee for the difference runs higher than the headline fee, as in artificial intelligence (0.70% versus 0.80%) and AI infrastructure and chips (0.70% versus 0.80%), while in cannabis it runs lower (0.80% versus 0.60%).
Beyond overlap with the index, some funds overlap heavily with each other. The data show 128 pairs of funds with portfolios more than half identical by weight. The closest examples include GII and IGF in infrastructure at 97% weight overlap, with fees of 0.40% and 0.37%, and IBB and IBBQ in biotech at 86%, with fees of 0.44% and 0.19%. Several semiconductor pairs also appear with overlaps in the mid-to-high seventies, including SOXQ and SOXX at 83% and FTXL and SOXX at 78%. In cases like these, holding both funds in a pair is close to holding one of them twice, though the fees attached to each side of a pair can differ.
Return patterns over the one-year period varied widely by theme, from semiconductors at +64.4% median total return to blockchain and crypto equities at −34.7%, with the number of funds beating the S&P 500 also ranging from 9 of 9 in semiconductors to 0 of 13 or more in several other themes. These numbers describe what happened in the period measured and are not a measure of overlap or cost.
Readers can look up any individual fund's in-index weight, active share, fee, and its closest overlapping pairs on ETFIQ's fund pages.