We report results of an investigation of interdiffusion in GaAs/Ga0.82In0.18As strained single quantum wells. Wells of width 12–100 A˚, grown by organometallic vapor phase epitaxy, were subjected to 10 s rapid thermal anneals of 830–950 °C, and shifts in the electron‐to‐heavy‐hole transition energies were detected by 4 K photoluminescence. We employed a powerful computer model to relate postdiffusion well shape to changes in photoluminescence energies, enabling estimation of diffusivity. Interdiffusion rates of 1×10−16–2×10−14cm2/s and activation energies of 3.1–3.8 eV were obtained.