XBI provides exposure to US biotech stocks, as defined by GICS, from a universe that invests across the market-cap spectrum. The fund equal-weights its portfolio, which in turn emphasizes small- and micro-caps and greatly reduces single-name risk. Thus, the weighted-average market-cap is much smaller than some competitors. Unlike other funds in this segment, XBI is a pure biotech play, with relatively small pharma overlap. The index is rebalanced quarterly.