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High resolution Rutherford Backscattering in combination with channeling and Transmission Electron Microscopy were used to study the fluence dependence of initial damage and residual defects of high‐temperature (900 °C) Se+‐implanted GaAs. It is found that the number of displaced atoms increases linearly as a function of dose, until the layer becomes amorphous. The damage profile extracted by using a single scattering theory is in good agreement with a Monte Carlo computer simulation when the ion dose is below that required to amorphize the layer. After annealing at 900 °C for 15 min, complete recovery of the damage has been observed for samples with 5×1012 cm-2 and 1×1013 cm-2. The samples with higher doses show some residual disorder which has been identified as dislocation loops and small precipitates. Electrical measurements reveal that highest activation efficiency is obtained for 1×1013 cm-2, which reduces drastically at higher doses. However, the activation efficiency for all doses increases with anneal temperature. The depth profile of the carrier concentration N showed that N is highest near the surface, decreases with increasing depth up to about 500 Å, and becomes nearly flat until it falls off near the substrate. The mobilities are found to be very low near the surface (≪1000 cm2/ V sec), but they increase to larger values (≳3000 cm2/V sec) at some depth below the surface.