We have investigated photoexcited carrier lifetimes in arsenic‐ion‐implanted semi‐insulating GaAs by time‐resolved reflectivity measurements. Subpicosecond carrier lifetimes (220 to 550 fs) which do not exhibit apparent dosage dependence for samples bombarded with 200 keV arsenic ions at increasing dosages in the range of 1012and 1016ions/cm2are reported. The shortest carrier lifetime was observed for the sample irradiated at 1013ions/cm−2. These are the shortest lifetimes ever observed for ion‐damaged GaAs and comparable to those of low‐temperature molecular beam epitaxially grown GaAs, which is also nonstoichiometric with excess‐arsenic‐related, deep‐level defects. ©1995 American Institute of Physics.