A thematic ETF is sold as a way to reach a specific idea, but the holdings often reach further back into the market than the label suggests. Across 380 funds, the typical thematic ETF holds 29% of its weight in stocks that the S&P 500 already owns, and 74 of those funds are more than sixty percent index names by weight. The measure used here is active share, which shows how much of a portfolio differs from the S&P 500; a fund with a low in-index weight and high active share is built mostly from names outside the benchmark, while a fund with a high in-index weight is, to that degree, a repackaged slice of the market it claims to look past.
The theme tables show this varies widely. Energy security and critical technology has a median 86% of its weight already in the S&P 500, alongside a median active share of 95%. AI infrastructure and chips sits at 63% in-index, and semiconductors at 66%, both still carrying active share above 80%. At the other end, gold miners, silver miners, and cannabis show 5%, 2%, and 0% in the S&P 500, with active share at or near 100%, meaning those portfolios are built almost entirely from names the benchmark does not hold.
Fees sit at a median 0.60% across 406 funds in 54 themes. When the fee is measured only against the part of each portfolio that differs from the S&P 500, the median fee for that difference is also 0.60%. In some themes the two numbers separate: biotech charges a median 0.50% overall but 0.30% for the differing portion, while cloud and software, artificial intelligence, and several others show the fee for the difference running higher than the headline fee, since the index-like portion of the portfolio is doing less work than the fee implies.
Beyond overlap with the S&P 500, some thematic funds overlap heavily with each other. The data finds 139 pairs of funds with portfolios more than half identical by weight, meaning that holding both is close to holding one of them twice. The listed pairs span several themes: SOXQ and SOXX in semiconductors show 86% weight overlap at fees of 0.19% and 0.33%; AUAU and GDX in gold miners show 84% overlap at 0.35% and 0.51%; ORBX and MARS in space show 81% overlap at 0.50% and 0.75%. EVMT and PDBA, in electric vehicles and batteries, show the highest overlap in the table at 97%, with matching fees of 0.59% each.
One-year returns varied by theme, from semiconductors at +99.3% and genomics and gene editing at +83.3% to nuclear and uranium at −12.8% and streaming and live entertainment at −22.7%. The "beat the S&P 500" column shows how many funds in each theme outran the index over one year, out of how many were measured; semiconductors shows 9 of 9, defense shows 0 of 14, and several small themes show single-fund counts.
On the live desk, a reader can look up any fund's current in-index weight, active share, and fee for the difference, and check whether its listed overlap pair still shows the same weight overlap today.