The small mass of light holes in strained quantum wells leads to high mobility at low fields. However, at high fields, the holes become hot and populate the heavy hole band, thereby greatly reducing their mobility. An analysis shows that the high‐field mobility primarily depends on Δ, the strain splitting of the light and heavy holes, and ℏω0, the optical phonon energy. If Δ<ℏω0, the light holes transfer to the heavy hole band at relatively low power and small fields. If Δ≊ℏω0, the low‐field mobility is greatly enhanced without producing negative differential mobility at high fields. If Δ>ℏω0, the high mobility persists until the applied power per carrier P exceeds a characteristic power P0 . Above this power, negative differential mobility (a Gunn effect) occurs when the light holes transfer to the heavy hole band. For thin p‐doped In0.2 Ga0.8 As/GaAs single‐strained quantum wells, Monte Carlo calculations show that P0 ≊5×10−8 W/carrier.