Depth profiles of Se‐implanted GaAs samples have been measured using secondary ion mass spectrometry (SIMS). Analyses performed on liquid‐nitrogen and room‐temperature implants into Cr‐doped substrates indicate that Se diffusion during subsequent heat treatment is negligible when the samples are annealed at 1000 °C for 15 min. A 12‐h anneal at 1000 °C does, however, produce a diffused profile but with a diffusion constant of 2.8×10−15cm2/sec as compared with the value 1×10−13cm2/sec for thermal diffusion of Se at this temperature.