The Schottky barrier height ofinsituepitaxial aluminum on AlxGa1−xAs was measured as a function of aluminum mole fraction fromx=0 tox=1, usingI/V,C/Vand activation energy plots of current‐voltage dependence on temperature. The excellent electrical properties of the molecular beam epitaxy grown AlGaAs layers, with residual deep levels concentrations of less than 1014cm−3combined with theinsitudeposition of single‐crystal epitaxial aluminum resulted in extremely high quality Schottky diodes fromx=0 (GaAs) tox=1 (AlAs) with accurately exponential current‐voltage characteristics over up to 10 decades and with ideality factors less than 1.03. Both theC−2−Vand activation energy plots were linear and yielded barrier heights in very good agreement with theI/Vones. The near‐ideal characteristics of these diodes were compared with several models of Schottky barrier formation and the dependence of the Schottky barrier height on the aluminum mole fraction was found to agree with the anion vacancy model within 10–20 meV, with a maximum deviation of 46 meV.