The effect of room‐temperature electron beam irradiation on the Al‐Ga interdiffusion at GaAs/AlGaAs quantum well heterointerfaces is investigated with low‐temperature cathodoluminescence spectroscopy. The interdiffusion is enhanced by defects generated through an irradiation with a 400 keV electron beam. After room‐temperature irradiation with a dose of ∼1.5×1017–2.5×1017/cm2and subsequent rapid thermal annealing at 900 °C for 1 min, an interdiffusion length of 3–5 A˚ is obtained. The electron beam induced damage tends to saturate with increasing irradiation dose, and the formation of defect cluster at high dose limits the defect introduction and, thus, the interdiffusion at the interface.