Key Takeaways
- • S Fund assets total $117.4 billion as of December 31, 2025, with a low expense ratio of 5.1 basis points, making it a cost-effective vehicle for small-to-mid-cap U.S. equity exposure.
- • BlackRock and State Street Global Advisors serve as the asset managers for the S Fund, which tracks the Dow Jones U.S. Completion Total Stock Market Index.
- • Top holdings include Snowflake, Marvell Technology, Cloudflare, and Roblox, reflecting concentration in technology and growth-oriented small-to-mid-cap stocks.
- • The S Fund has delivered strong historical performance, including 31.85% gains in 2020 and 11.97% gains in November (year unspecified), positioning it as an attractive equity diversification tool within the Thrift Savings Plan.
- • The fund provides portfolio diversification benefits when combined with other TSP equity funds (C, I Funds), reducing exposure to single-market-segment risk across domestic equities.
Summary
The S Fund, formally known as the Small Capitalization Stock Index Fund within the Thrift Savings Plan, remains a cornerstone holding for federal employees and institutional investors seeking exposure to small-to-mid-cap U.S. equities. The fund holds $117.4 billion in assets and is passively managed to track the Dow Jones U.S. Completion Total Stock Market Index, which includes U.S. companies not represented in the S&P 500 Index.
Asset management is distributed between BlackRock Institutional Trust Company and State Street Global Advisors Trust Company, with the fund maintaining an exceptionally low total expense ratio of 5.1 basis points per $1,000 account balance. This cost structure has made the S Fund an attractive vehicle for institutional and retail investors seeking broad small-to-mid-cap market exposure without substantial fee drag. The fund's inception dates to May 1, 2001, establishing over two decades of track record.
Recent portfolio composition reflects a technology-heavy weighting. The top ten holdings as of December 31, 2025, are led by Snowflake Inc., Marvell Technology Inc., Cloudflare Inc., Veriv Holdings, Roblox Corp., Alnylam Pharmaceuticals, Ferguson Enterprise, and Cheniere Energy Inc. This concentration in technology and growth-oriented equities has contributed to the fund's strong historical performance metrics. The S Fund gained 31.85% in 2020 and posted an 11.97% return in November, demonstrating meaningful upside capture in equity cycles.
Within a diversified TSP portfolio strategy, the S Fund serves an important role when combined with the C Fund (large-cap) and I Fund (international) to achieve broad market segmentation without overlap. This structure allows investors to systematically capture returns across different market capitalizations and geographies while managing systemic equity risk through index-based passive management.
Asset management is distributed between BlackRock Institutional Trust Company and State Street Global Advisors Trust Company, with the fund maintaining an exceptionally low total expense ratio of 5.1 basis points per $1,000 account balance. This cost structure has made the S Fund an attractive vehicle for institutional and retail investors seeking broad small-to-mid-cap market exposure without substantial fee drag. The fund's inception dates to May 1, 2001, establishing over two decades of track record.
Recent portfolio composition reflects a technology-heavy weighting. The top ten holdings as of December 31, 2025, are led by Snowflake Inc., Marvell Technology Inc., Cloudflare Inc., Veriv Holdings, Roblox Corp., Alnylam Pharmaceuticals, Ferguson Enterprise, and Cheniere Energy Inc. This concentration in technology and growth-oriented equities has contributed to the fund's strong historical performance metrics. The S Fund gained 31.85% in 2020 and posted an 11.97% return in November, demonstrating meaningful upside capture in equity cycles.
Within a diversified TSP portfolio strategy, the S Fund serves an important role when combined with the C Fund (large-cap) and I Fund (international) to achieve broad market segmentation without overlap. This structure allows investors to systematically capture returns across different market capitalizations and geographies while managing systemic equity risk through index-based passive management.
Go deeper than the headline
Research every firm in this story, track the ones that matter and get the daily briefing — free for 7 days.