Ion beam assisted etching (IBAE) is a dry etching technique in which the sputter etching component of an argon ion beam and the chemical etching component supplied by a Cl2gas flux are independently controlled. This technique has been used to obtain anisotropic etching of GaAs with minimal surface damage over areas of a few square millimeters. The results reported here are achieved with an improved IBAE system designed to etch considerably larger areas. The system accurately and uniformly delivers reactive gas flux to the sample giving uniform etching rates over the 2‐cm‐diam area exposed to the ion beam. When the sample is exposed to high reactive gas fluxes, equivalent to a pressure of 1×10−2Torr, and 1 to 2 keV Ar+ions at 1 mA cm−2, etching rates of 5 to 10 μm/min are obtained making etched through‐holes in GaAs wafers realizable. Control of the ion beam collimation and the reactive gas flux allow for accurate control of undercutting making submicrometer etched structures in GaAs with aspect ratios>35:1 easily obtainable. In addition, damage studies of the ion beam assisted etched GaAs surfaces shows a low trap density in the range of 1013cm−3as determined by deep level transient spectroscopy (DLTS). The improved system uses two gas jets to supply the chemically reactive flux and a liquid N2cooled shroud to trap the unused reactive gas. The absolute reactive flux impinging on the sample is determined with a capacitance monometer and the ion beam collimation is controlled by varying the ion gun to sample distance.