Schottky barrier heights for aluminum‐(100) GaAs diodes with and without an interfacial native oxide layer have been evaluated using Norde’s method of current‐voltage analysis. Barrier heights determined by Norde’s method on sputter‐annealed, oxide‐free substrates are systematically lower (0.53–0.59 eV) than values determined by photoresponse measurements (0.78±0.03 eV). Anomalous structure in the form of a second minimum was observed in the Norde plots for unsputtered substrates on which a thin native oxide was present. The barrier heights obtained from the second minimum observed at high forward bias (∼0.75 V) were 0.90–0.95 eV, whereas photoresponse measurements indicated barriers of 1.00±0.01 eV.