Low temperature photoluminescence and Auger electron spectroscopy have been used to study chemical-vapor deposited SiO(2) and Si(3)N(4) layers as encapsulants for high temperature annealing of GaAs. Silicon dioxide or silicon oxynitride layers allow out-diffusion of Ga, while suitably prepared rf plasma deposited Si(3)N(4) layers can be used to anneal GaAs with negligible Ga outdiffusion.