Infrared reflection and transmission measurements were used to study the thermally induced regrowth of (100) oriented, Be‐implanted GaAs samples. The samples used in this study were implanted at low temperature (−100 °C) with 250‐keV Be ions to a fluence of 6×1015cm−2. The samples were postannealed at temperatures ranging from 100 to 550 °C. Isochronal and isothermal annealing at a series of temperatures between 180 and 240 °C were performed. Infrared reflection spectra were analyzed by using a three or four layer dielectric model. Analysis of the annealing data suggests that an amorphous layer first anneals to a second metastable amorphous state and then becomes a damaged crystalline layer after annealing at 220 °C for 12 h. The observed regrowth is not by a simple epitaxial process. After annealing at 400 °C for 1 h, the damage in the layer is reduced sufficiently for the refractive index to recover almost to the preimplantation value. On annealing at 450 °C free carriers are observed. From the measured average regrowth rate for the amorphous layer at various anneal temperature, an effective activation energy is estimated to be about 1.45 eV. This compares with activation energies of 2.3 eV for Si and 2.0 eV for Ge.