The barrier height at the anodic oxide/GaAs interface has been determined by internal photoemission of the metal‐oxide‐semiconductor structures. The height of the potential barrier between the oxide and GaAs is found to be 2.62±0.05 eV for as‐grown and 2.39±0.05 eV for hydrogen‐annealed specimens. Quantum yield below the photoemission threshold is interpreted in terms of electron emission from interface states at energies above midgap of GaAs.