Epitaxial Al Schottky barriers were grown on molecular beam epitaxy AlxGa1−xAs layers without exposure to air. Al is deposited on As‐rich surfaces of AlxGa1−xAs form AlAs interfacial layers modifying the intrinsic Shottky barrier height. The difference between In‐AlGaAs and Al‐AlGaAs barrier heights agree well with their work function difference. Shottky barriers prepared on AlGaAs surfaces with the lowest As‐coverage obey the common anion rule in the regionx⩽0.3. Above this value oxygen‐related elements appear to dominate.