Schottky barriers of Au, Al, and Sb onn‐ andp‐type layers of Al0.5Ga0.5As0.05Sb0.95have been studied. The Schottky barriers are high for Au (1.3 eV) and Al (1.2 eV) deposited onn‐type material and very low for these metals onp‐type layers. The behavior of Sb is unique with the barrier heights being 0.6–0.7 eV for bothn‐ andp‐type AlGaAsSb. The reason for the surface Fermi‐level pinning for Au and Al could be related to a predominance of Ga‐antisite–type native acceptors at the surface, which is not the case for Sb. Sulfur treatment of the surface is shown to decrease the barrier height for Au and to increase greatly the photosensitivity of Au Schottky diodes. The same effect is observed after treatment in a hydrogen plasma. In the latter case, changes in the Schottky barrier height are correlated with passivation of native acceptors in the bulk of the Al0.5Ga0.5As0.05Sb0.95.