Stress generated on GaAs‐SiO2interface during annealing and the effect of this stress on tin diffusion in GaAs have been investigated using laser Raman spectroscopy. It was found that compressive stress exists on the surface of GaAs after annealing, which increases with increase of the SiO2cap layer thickness. The compressive stress on GaAs is generated during annealing and is due to the difference of the thermal expansion coefficients between GaAs and SiO2. The increase of compressive stress on the surface of GaAs decreases the diffusion coefficient of tin in GaAs. This occurs due to the reduction of Ga vacancy in a compressively stressed sample from the equilibrium Ga vacancy of an unstressed sample. ©1996 American Institute of Physics.