Diffusion of indium markers atT=900 °Chave been measured in undoped and Te-doped GaAs epilayers grown by organometallic vapor phase epitaxy. The diffusivity was found to be a linear function of electron concentration over the rangen=2×1017–1.5×1019 cm−3.The results are consistent with the interdiffusion of AlAs–GaAs superlattices, and the diffusivities of In and Al in GaAs at 900 °C are found to be essentially identical within experimental noise. The results strongly suggest that group III interdiffusion in GaAs is controlled by a Ga vacancy with a charge of−1.©1997 American Institute of Physics.