This paper reports the results of a modulated ion beam study of the ion‐assisted etching of Si using Cl2gas and Ar+ions. These experiments were designed to study the kinetic mechanism of the ion‐enhanced surface reaction of Si with Cl2, which is thought to be responsible for anisotropic etching of Si in practical plasma systems. Pulses of Ar+ions (typically 12 ms long) were incident on the surface with ion fluxes ranging up to 4.5×1014ions/cm2 s and ion energies between 0.3 and 3 keV. Chlorine fluxes were varied between 2×1012and 4×1014molecules/cm2 s. Products were detected with a quadrupole mass spectrometer and a comparison of the resulting modulated signals with the cracking pattern of SiCl4under the same conditions indicated that most of the Si left the surface in the form of SiCl4. The amount of Si removed from the surface depended linearly on the incident ion and increased with increasing chlorine up to a saturation limit. The time dependence of the product signals, measured by signal averaging, is not consistent with physical sputtering. A kinetic mechanism is discussed for this reaction.