The growth of GaN by HVPE has been analysed by means of a thermodynamical and kinetic study. Two mechanisms involved in the growth of (00.1) GaN HVPE have been deduced from the numerous experiments performed on (0 0 1) GaAs by the chloride method. The parameters of these two growth mechanisms have been resolved from the experimental variations of HVPE GaN growth rate. Experiments performed in conditions of expected fast etching by HCl, in a mixed H-2/N-2 carrier gas, led to a new growth mechanism by considering a combined Cl desorption by GaCl as GaCl2 and an etching by HCl. The apparent activation energy of the new Cl desorption reaction is the only new parameter introduced in the third growth mechanism. In this paper, we present the results obtained for the determination of a more accurate value of this new parameter. The growth rate was measured versus the growth temperature for different H-2 concentrations in the carrier gas. A quite good agreement was obtained between experimental and theoretical values. (C) 2003 Elsevier B.V. All rights reserved.