A new phenomenological model for the growth of GaAs in the GaCl/AsH3/HCl/H-2 vapour phase system is developed. The surface growth kinetics are modelled by taking into account the mechanisms of As and GaCl adsorption and chlorine desorption by H-2 into HCl. Two ad-species AsGaCl and AsGa interact on the surface through a reversible reaction, which is described through a modified two-particle Burton, Cabrera and Frank model. Kinetics data are determined by synthesising experimental and computed results. It is shown that when surface diffusion limitations can be neglected, the growth rate is reduced to a one-particle-like direct condensation expression, weighted by a sticking coefficient which takes into account the desorption frequency of the precursor AsGaCl and its reversible transformation into the crystal particle AsGa. Variations of the growth rate are discussed as a function of the ad-species surface coverage ratios and of the supersaturation of the vapour phase. (C) 2003 Elsevier B.V. All rights reserved.