Channeling and transmission electron microscopy have been used to investigate the parameters that govern the extent of damage in ion‐implanted GaAs and the crystal quality following capless furnace annealing at low temperature (∼400 °C). The implantation‐induced disorder showed a strong dependence on the implanted ion mass and on the substrate temperature during implantation. When the implantation produced a fully amorphous surface layer the main parameter governing the regrowth was the amorphous thickness. Formation of microtwins after annealing was observed when the initial amorphous layer was thicker than 400 A˚. Also, the number of extended residual defects after annealing increased linearly with the initial amorphous thickness and extrapolation of that curve predicts good regrowth of very thin (<400 A˚) GaAs amorphous layers produced by ion implantation. A model is presented to explain the observed features of the low‐temperature annealing of GaAs.