A look at thematic ETF holdings as of October 8, 2026 shows that much of what passes for a distinct bet is, by weight, already inside the S&P 500. Across 391 funds with the needed data, the typical thematic fund holds 32% of its portfolio in names the S&P 500 already owns, and 74 of those 391 funds are more than sixty percent index names. That means a meaningful share of thematic products are, for most of their weight, close cousins of the broad market index rather than something separate from it.
The pattern varies widely by theme. Energy security and critical technology shows a median of 85% in the S&P 500, and AI infrastructure and chips and Semiconductors both sit at 62% or higher. At the other end, Cannabis shows 0% in the S&P 500, Silver miners 2%, and Coal 0%. Active share, the measure of how much a fund's weights differ from the index, mirrors this: Semiconductors funds show a median active share of 85%, the lowest in the table, while most other themes cluster near 95% to 100%.
Fees do not track this overlap in a simple way. Across 54 themes and 419 funds, 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 fee for that difference is also 0.60%. Theme by theme, some funds with high index overlap carry low fees, such as Semiconductors at 0.30% headline and 0.40% for the difference, while others with similarly high overlap, such as Energy security and critical technology, sit at 0.50% and 0.60%. Low-overlap themes like Gold miners and Nuclear and uranium charge 0.50% and 0.70% respectively, with little consistent relationship to how much of the portfolio is distinct from the index.
Overlap between funds within the same theme is also common. The data identifies 131 pairs of funds whose portfolios are more than half identical by weight, meaning that holding both amounts to something close to holding one of them twice. The table of pairs includes PDBA and EVMT in Agriculture at 100% weight overlap, IBBQ and IBB in Biotech at 85%, and AUAU and GDX in Gold miners at 83%. Several Semiconductors pairs also appear, including SOXQ and SOXX at 82% and SHOC and SMH at 78%, each carrying different fees despite the similarity in holdings.
Fund count and return patterns differ across themes as well. Semiconductors funds beat the S&P 500 in 9 of 9 cases over one year with a median total return of +84.8%, while Defense funds did so in 0 of 14 cases with a median return of −9.1%. These numbers describe what happened in the period measured and are not an indication of what the same funds will do going forward.
Readers working from the live desk can check the in-index weight, active share, and fee numbers for any specific fund or theme as of the most recent filing date, since the numbers here are fixed to data as of October 8, 2026.