The intermixing of AlAs‐GaAs superlattices has been investigated as a function of Si concentration following anneals in the range of 500 to 900 °C. The superlattice samples were grown by molecular beam epitaxy and the near surface layers were doped with silicon at concentrations of 2×1017to 5×1018cm−3. Si and Al depth profiles were measured with secondary ion mass spectrometry (SIMS). The diffusion length and activation energy of Al as a function of silicon dopant concentration were derived from the SIMS data. In the temperature range studied a single activation energy for the Al diffusion of ∼4 eV was observed, and the Al diffusion coefficients increased rapidly with Si concentration.