Calculations of the high‐field properties of holes in Al0.45Ga0.55As are presented based on the ensemble Monte Carlo technique. It is shown that the hole drift velocity in AlGaAs is significantly below that in GaAs until saturation occurs. Despite the much larger energy band gap in Al0.45Ga0.55As, the hole ionization rate approaches that of GaAs at very high electric fields, >600 kV/cm. No significant hole impact ionization is observed below 300 kV/cm in Al0.45Ga0.55As. This is of importance to superlattice avalanche photodiodes made from the GaAs/AlGaAs material system.