The light beam induced current (LBIC) technique was used to characterize the interface formed by the wet oxidation of AlAs andAlxGa1−xAs(x=0.98and 0.95). LBIC scans were used to calculate the diffusion lengths of minority carriers both in the bulk and near these interfaces; and the corresponding interface recombination velocities were estimated. The interface recombination velocity at the oxide/semiconductor interface is3.13×105 cm/sfor AlAs, and1.90×104 cm/sforAl0.98Ga0.02As.It is found that the addition of gallium in the AlAs can significantly improve this property. ©1997 American Institute of Physics.