The interface of a GaAs/AlxGa1−xAs heterostructure grown by metalorganic chemical vapor deposition has been studied by photoluminescence spectroscopy by using a step‐etching technique. Luminescence peaks associated with vacancy complexes emitted from both GaAs and AlxGa1−xAs layers were observed, and these peaks were remarkably intense on both sides of the GaAs/AlxGa1−xAs interface region. This result can be explained by the accumulation of vacancies in the interface region. The cause of this vacancy accumulation at the interface is discussed.