What Is XBI? SPDR S&P Biotech ETF
Last updated July 2026
Short answer
XBI is the SPDR S&P Biotech ETF, a modified equal-weighted fund holding roughly 150 to 160 US biotechnology companies. It tracks the S&P Biotechnology Select Industry Index and charges a 0.35% expense ratio. Because it equal-weights rather than cap-weights, XBI gives small and mid-cap biotech far more influence than a cap-weighted fund like IBB, which makes it a higher-beta, more volatile way to own the sector and a favorite proxy for the broad biotech cycle.
XBI is issued by State Street Global Advisors (SPDR) and tracks S&P Biotechnology Select Industry Index. It charges a 0.35% expense ratio, holds approximately ~$8 billion in assets under management, yields about ~0.2%, and launched in January 2006.
What is XBI?
XBI is the SPDR S&P Biotech ETF, an exchange-traded fund offering broad exposure to the US biotechnology industry. It tracks the S&P Biotechnology Select Industry Index and charges a 0.35% expense ratio, holding roughly 150 to 160 companies across the sector.
What sets XBI apart is its modified equal-weight construction. Instead of letting a few large-cap biotechs dominate, the index assigns similar weights across its holdings and rebalances quarterly. That design makes XBI a diversified, high-beta expression of the biotech sector and a widely watched gauge of investor appetite for the space.
XBI holdings
Approximate weights as of mid-2026; refresh quarterly from State Street Global Advisors (SPDR)'s fund page. Each ticker links to its individual stock guide in Walnut.
| Rank | Ticker | Company | % of XBI | |
|---|---|---|---|---|
| 1 | MRNA | Moderna, Inc. | ~1.5% | |
| 2 | APGE | Apogee Therapeutics, Inc. | ~1.4% | |
| 3 | KYMR | Kymera Therapeutics, Inc. | ~1.4% | |
| 4 | VKTX | Viking Therapeutics, Inc. | ~1.3% | |
| 5 | ERAS | Erasca, Inc. | ~1.3% | |
| 6 | PRAX | Praxis Precision Medicines, Inc. | ~1.2% | |
| 7 | TWST | Twist Bioscience Corporation | ~1.2% | |
| 8 | ORKA | Oruka Therapeutics, Inc. | ~1.2% | |
| 9 | MIRM | Mirum Pharmaceuticals, Inc. | ~1.2% | |
| 10 | RYTM | Rhythm Pharmaceuticals, Inc. | ~1.2% |
XBI's portfolio is spread thin by design, with top positions typically weighing only around 1% to 1.5% each. Recent holdings have included Moderna, Apogee Therapeutics, Kymera Therapeutics, Viking Therapeutics, Twist Bioscience, Praxis Precision Medicines, and Rhythm Pharmaceuticals.
The fund spans large-cap biotechs, commercial-stage companies, and a large tail of clinical-stage drug developers. Because so many holdings are emerging, pre-profit companies, the roster changes frequently as names graduate, get acquired, or fall out of the index during quarterly reconstitution.
XBI vs IBB
The most common comparison for XBI is iShares' IBB. Both target biotech, but IBB is market-cap-weighted and dominated by a handful of large-cap biotechs, which makes it steadier and more concentrated at the top.
XBI equal-weights its holdings, giving small and mid-cap drug developers far more influence. That makes XBI more volatile and more sensitive to the broad biotech cycle, while IBB behaves more like a bet on the sector's established leaders. Investors often choose between them based on how much small-cap exposure they want.
Performance and outlook
XBI's returns are driven heavily by sentiment toward small and mid-cap biotech, clinical-trial outcomes, FDA decisions, and merger activity. It has moved through several dramatic booms and busts, reflecting how binary and news-driven the underlying companies can be.
The long-term case rests on continued drug innovation, an active mergers-and-acquisitions market for smaller biotechs, and a favorable funding environment. In the near term, XBI is likely to stay volatile, with interest rates and risk appetite playing an outsized role in its swings.
Is XBI a good fit?
XBI suits investors who want diversified, high-beta exposure to the biotech sector, especially its small and mid-cap end, and who can stomach significant volatility. Its equal-weight design makes it more of a satellite sector position than a core holding, typically sized as a slice of a broader portfolio.
Walnut is not an investment adviser. This is descriptive information, not a recommendation. Whether XBI belongs in your portfolio depends on your goals, time horizon, risk tolerance, and existing holdings, so weigh those factors or consult a licensed professional before deciding.
How to buy XBI
XBI trades on the NYSE Arca and can be purchased through brokerages such as Robinhood, Fidelity, Charles Schwab, and Public. Many of these support fractional shares, so you can start with a small dollar amount rather than buying a full share.
You can also connect your existing brokerage to Walnut to track XBI alongside your other positions and build a basket around a biotech thesis. Walnut helps you monitor how the holding aligns with your target weights over time while your trades stay at your broker.
The bottom line on XBI
XBI is the go-to equal-weighted biotech ETF, giving outsized exposure to small and mid-cap drug developers at a reasonable 0.35% fee. It is volatile and news-driven, so it fits as a satellite sector position for investors who want biotech beta rather than a core holding.
More on XBI
Whether XBI is worth buying today depends more on your time horizon and what you already hold than on any single call. We walk through valuation, concentration, and what would have to be true for it to outperform from here in is XBI a buy?
XBI yields ~0.2% as of mid-2026, paid by passing through the dividends of its underlying holdings. For the payout schedule, history, and how the distributions are taxed, see XBI dividend: yield and schedule.
Build a portfolio around XBI with Walnut
Use XBI as your core holding, then let Walnut's AI propose thematic satellites: AI infrastructure, dividend growth, clean energy, whatever you believe in. Connect your broker, build the basket in conversation, track it as one unit.
FAQ
What is XBI?
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XBI is the SPDR S&P Biotech ETF, a fund that holds roughly 150 to 160 US biotechnology companies. It tracks the S&P Biotechnology Select Industry Index on a modified equal-weight basis and charges a 0.35% expense ratio, giving broad, diversified exposure across large, mid, and small-cap biotech.
Who issues XBI and what does it track?
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XBI is issued by State Street Global Advisors under its SPDR brand and tracks the S&P Biotechnology Select Industry Index. That index is a modified equal-weighted measure of the biotechnology segment of the S&P Total Market Index, so smaller companies carry weight comparable to larger ones.
What does XBI hold?
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XBI holds roughly 150 to 160 US biotech stocks spread fairly evenly, with top positions typically only around 1% to 1.5% each. Recent holdings have included Moderna, Apogee Therapeutics, Kymera Therapeutics, Viking Therapeutics, Twist Bioscience, and Rhythm Pharmaceuticals. Its composition shifts often as clinical-stage names move in and out.
What is the difference between XBI and IBB?
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Both cover biotech, but XBI is modified equal-weighted while iShares' IBB is market-cap-weighted. IBB is dominated by a few large-cap biotechs, whereas XBI spreads exposure across many small and mid-cap drug developers. That makes XBI more volatile and more of a bet on the broad biotech cycle than on the sector's giants.
What is XBI's expense ratio?
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XBI charges an expense ratio of 0.35%, or about 3.50 dollars a year per 1,000 dollars invested. That is reasonable for a specialized sector ETF and comparable to peers like IBB. It is higher than a broad market index fund but standard for targeted industry exposure.
Does XBI pay a dividend?
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XBI pays only a small distribution, with a yield of roughly 0.2%. Most biotech companies, especially the clinical-stage names that fill the fund, reinvest capital into research rather than paying dividends. Investors buy XBI for growth and sector exposure, not income.
How do I buy XBI?
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XBI trades on the NYSE Arca and can be bought through brokerages like Robinhood, Fidelity, Charles Schwab, and Public, most of which support fractional shares. You can also connect your broker to Walnut to track XBI alongside your other holdings and build a basket around a biotech thesis.
How big is XBI?
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XBI has roughly 8 billion dollars in assets under management as of mid-2026, making it one of the largest and most liquid biotech ETFs. Its size and tight trading spreads make it a common vehicle for both long-term investors and traders expressing a view on the sector.
Is XBI a good investment?
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Whether XBI fits depends on your goals, risk tolerance, and portfolio. Biotech is a volatile, news-driven sector, and XBI's equal-weight tilt amplifies swings from small-cap clinical results. Walnut is not an investment adviser, so treat this as descriptive information and consider your own situation before investing.
When was XBI created?
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XBI launched in January 2006, issued by State Street under the SPDR brand. It has a long track record across multiple biotech booms and busts, which has made it one of the most widely referenced barometers of sentiment toward the biotechnology sector.
Why is XBI so volatile?
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XBI equal-weights its holdings, so small and mid-cap clinical-stage biotechs carry meaningful weight. Those stocks can move sharply on trial results, FDA decisions, and merger news. Because many holdings are pre-profit and binary-outcome, the fund tends to be more volatile than the broad market or a cap-weighted biotech fund.
Is XBI a good way to trade the biotech cycle?
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Many investors use XBI as a proxy for the broad biotech cycle precisely because it is equal-weighted and liquid. It tends to reflect risk appetite for small and mid-cap drug developers, so it often leads or lags the market during biotech booms and downturns.
Does XBI focus on small-cap biotech?
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XBI is not exclusively small-cap, but its modified equal-weight design gives small and mid-cap biotech far more influence than a cap-weighted fund would. As a result, its returns are driven more by the fortunes of emerging drug developers than by the sector's largest, most established companies.
How often does XBI rebalance?
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The underlying S&P Biotechnology Select Industry Index rebalances quarterly, resetting weights back toward equal and adding or removing companies as the biotech universe changes. This regular reconstitution keeps the fund broadly diversified and prevents any single winner from dominating for long.
How do I compare XBI to similar ETFs?
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Put a few fields side by side: the expense ratio (fees compound over decades), the index or strategy it tracks, the top holdings and how much they overlap with what you already own, the dividend yield, and the AUM, liquidity, and bid-ask spread that affect trading costs. For index funds, tracking error (how closely it follows its index) and tax efficiency matter too. XBI's figures are above; the full method is in Walnut's guide on how to compare ETFs.
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Walnut is informational, not investment advice. Holdings weights and fund statistics on this page are approximations stamped to mid-2026; verify current figures against State Street Global Advisors (SPDR)'s fund page or your broker before investing.