Zinc and selenium implantations have been performed in Cr‐doped semi‐insulating GaAs. We show that all zinc and selenium implanted impurities are electrically active after annealing at 900 °C. But, in addition to the implantation distribution, there is a distribution induced by the chromium outdiffusion during annealing leading to a Cr‐depleted zone, which can become conductive. By taking into account these distributions, the electrical measurements may be explained.