A two-dimensional chemically assisted ion beam etching model (CAIBE) has been developed in connection with the experiment. The effects of the chlorine flow rate and the GaAs substrate temperature have been studied. For a low Cl-2 flow rate (Q(Cl2) < 2 sccm), the simulation results show that the GaAs etching rate is mainly controlled by the physical etch process. Over this value, the ion assisted mechanism becomes preponderant. In the case of the band etch through the mask, the increase of the Cl-2 flow rate and the temperature contribute to the improvement of the etching anisotropy and elimination of microtrenching. A good agreement between the simulations and the experiments concerning the etching rate and the etch profiles through the mask versus the flow rate and temperature have been obtained. (c) 2005 American Vacuum Society.