The kinetics of implantation enhanced interdiffusion at GaAs‐GaxAl1−xAs interfaces is investigated by cathodoluminescence and transmission electron microscopy. Localized Ga+implantation leads to enhancement of the interdiffusion by about two orders of magnitude at 950 °C. A complete recovery of the optical quality of the material and local alteration of the band gap is observed after rapid thermal annealing. The role of intrinsic interdiffusion is identified. Control of the interdiffusion kinetics has allowed the fabrication of ultrasmall structures with good optical properties.