There is increasing technological interest in using Cl2and Cl‐containing compounds in the dry plasma etching of III–V semiconductors. This paper presents a study of the ion‐assisted etching of GaAs by Cl2using a modulated ion beam technique to gain insight into the kinetic mechanism of this process. The etching rate increases with increasing ion energy (0.3–3 kV) and depends linearly on ion flux (1.0–10.0×1014ions cm2 s). The etching rate increases with increasing Cl2pressure up to a saturation limit near 2×10−6Torr. This saturation limit is independent of the ion flux coincident on the surface within the range studied. The ion‐enhanced etching rate decreases with increasing sample temperature over the range 300–500 K. Major etch products are AsCl3and GaCl2(and possibly GaCl), and the time dependence of the increase in these mass spectrometer signals following the initiation of the ion pulse is consistent with all of the products having a most probable translational energy of ∼0.14 eV. There is an additional delay in the appearance of the AsCl3signal which roughly corresponds to a first order reaction with an associated time constant of 1.1 ms. One possible kinetic mechanism for the ion‐enhanced etching is proposed which involves the surface reactions of Ga and AsCl with adsorbed chlorine. In this model, the ∼1 ms delay in the appearance of the AsCl3is attributed to the lifetime of potential energy excitation caused by the ion.