Emission mechanisms and reaction rates for the ion‐assisted etching of GaAs(100) have been studied in detail using energetic argon ions and chlorine gas. Ion energies of 500 and 1000 eV were used with chlorine/argon ion surface‐flux ratios of 1–120. Themajormolecular etchant products were found to be GaCl2and AsCl3. Gas phase products were detected at different flight distances to investigate the nature of surface residence times. It is concluded, based on these measurements, that GaCl2emission is best interpreted in terms of the collisional‐cascade sputtering model for the specific range of ion energies and surface‐flux ratios studied. Using a similar analysis, it is concluded that AsCl3may be emitted by either the thermal desorption or the collisional‐cascade mechanisms, with the former favored in the range of higher surface‐flux ratios and lower ion energies. Furthermore, the thermal desorption of AsCl3appears to follow a first‐order surface process. Comparison of our data with those of others indicates general agreement. However, more extended analysis based on a broader and more intensive data base leads to some important distinctions among the final conclusions regarding the emission mechanisms.