The diffusion of Vanadium has been studied in V-doped GaAs layers (GaAs:V) grown by Metal-Organic Chemical Vapour Deposition (MOCVD) using secondary ion mass spectroscopy (SIMS). The vanadium (V) concentration profiles of sandwiched structures made of alternatively undoped and V doped GaAs layers have shown a concentration independent diffusion coefficient (D-V) for varying V doping levels from 10(18)s to 10(19)cm(-3). Measurements of D-V at 550, 615 and 680 degreesC indicate that the temperature dependence of D-V can be represented by the Arrhenius equation: D-V = 2.4 x 10(-6) exp(-1.51 eV/k(B)T)cm(2) s(-1). It is suggested that V diffuses via interstitial sites. (C) 2004 Elsevier B.V. All rights reserved.