In0.53Ga0.47As/ In0.52Al0.48As single quantum well structures grown by molecular beam epitaxy were pulse annealed by a halogen lamp to determine the stability of their optical properties after such thermal treatment. The annealing time and temperature were 5 s and 650–850 °C, respectively. The shift in energy of the main peak in the low‐temperature photoluminescence spectra was modeled by considering Al‐Ga interdiffusion at the heterointerface and solving the appropriate Schro¨dinger equation for this region. The estimated interdiffusion constantsDare ∼10−16–10−15cm2/s in this temperature range, which are almost three orders higher than the corresponding values reported for GaAs/ AlxGa1−xAs. For longer annealing times, up to 30 min, the linewidth (full width at half‐maximum) of the excitonic transition in the 11 K photoluminescence spectrum continuously decreased from 12.5 to 7.7 meV, while the intensity maintained a high value.