The effects of implantation and annealing on an AlAs-GaAs superlattice grown by OMCVD is examined with SIMS (secondary ion mass spectrometry). Several 180 keV 28Si+ implants, with doses ranging from 3 × 1013 to 3 × 1015 cm−2, are examined before and after a three hour 850 C anneal. While the implantation by itself causes some intermixing in the vicinity of the projected range, the 850 C thermal anneal induces significant mixing at depths well beyond the implant range. In the region of maximum implant damage, however, the post-thermal mixing effect is inhibited. Depth dependent diffusion lengths of Al and Si are derived from the SIMS data. The diffusion coefficient of Si is markedly enhanced in the mixed regions.