The deactivation of electrically active ion‐implanted arsenic in silicon during cooling‐down, following rapid thermal annealing, has been studied. Chemical and carrier‐density profiles were measured as a function of annealing temperature and cooling rate. It is found that the cooling rate has a pronounced effect on the maximum carrier concentration which can be obtained at a given temperature. It is further demonstrated that the equilibrium carrier concentration at a given temperature is higher than the previously accepted values.