We have modelled the incorporation of As antisite defects in GaAs during epitaxial growth. The model assumes that the antisite is introduced as a result of the incorporation of an As, molecule occupying a Ga site without being dissociated. The antisite incorporation is thermally activated with an activation energy of 1.4 eV and a frequency factor of 10(12) s(-1), resulting in the nondissociation of As-2 molecules on the surface. The results of the modelling are compared with experimental data obtained by molecular beam epitaxy at low temperature and by vapor phase techniques at high temperature. The concentration of antisites has been determined versus the growth rate and the substrate temperature using electrical methods, infrared absorption and through the change of the lattice mismatch. The temperature and the growth rate dependences of Arsenic antisite obtained from our model are in agreement with the experimental results, the fitting parameters being independent of the growth conditions. (C) 2002 Elsevier Science B.V. All rights reserved.