Rapid thermal annealing has been used to study the activation mechanism of zinc ions implanted into GaAs. The data divide into two parts, a time‐dependent and a time‐independent regime. Analysis of these regimes suggests that inactive zinc becomes electrically active by local diffusion to an unoccupied gallium vacancy, the energy for this process being 1.1 eV. The time‐independent regime produces another energy of 0.37 eV which is suggested to be the energy required to place a zinc atom onto a gallium vacancy.