Abstract: A method of manufacturing GaAs semiconductor devices includes the steps of emplacing doping impurities by ion implantation on at least one surface of a GaAs substrate, and a step of annealing to remove damage resulting from the implantation of the impurities in the GaAs material. Prior to the annealing, a silicon capping layer is deposited on the surface by either sputtering, evaporation, or vapor deposition to a thickness of 100-10,000 angstroms. Subsequent to the annealing, the silicon capping layer is removed by etching. The silicon cap prevents out-diffusion of arsenic from the GaAs, and has a coefficient of thermal expansion which is sufficiently close to that of the GaAs to inhibit the formation of cracks in the capping layer.