ZnSe samples were grown on Zn and Se pre-deposited GaAs substrates. Thermal diffusion of elements across the ZnSe/GaAs interface was investigated, using secondary ion mass spectroscopy (SIMS). Diffusion of Ga atoms across the interface was observed for Zn pre-treated substrates, whereas Se pre-treatment of the GaAs substrate prevents thermal diffusion of Ga across the interface. This effect believed to be due to formation of GaAsxSey "barrier layers" at the ZnSe/GaAs interface. The Ga diffusion coefficients at annealing temperatures of 400, 500 and 600 degreesC were found to be 2.1 x 10(-16), 1.9 x 10(-15), and 2.2 x 10(-14) cm(2)/s, respectively. The thermal diffusion of other elements across the interface was not observed within the depth resolution limit of SIMS analysis. (C) 2002 Elsevier Science B.V. All rights reserved.