Bromine ion-beam-assisted etching produces smooth vertical sidewalls in GaAs wafers with substrate temperatures in the range of 20–200 °C and smooth vertical sidewalls in InP wafers with substrate temperatures in the range of 150–200 °C. Etch rates can be varied from several nm/min to 0.16 μm/min through the bromine flow rate, Ar+ ion beam density and energy, and the substrate temperature. The etching rate ratios of bromine-only etching (no Ar+ ion beam) to argon ion-beam-assisted bromine etching to argon ion etching (no bromine) with an ion beam density of 40 μA/cm2 and ion beam energy of 500 V were measured to be 11.5:23:1 and 16:125:1 at a substrate temperature of 200 °C and 2:42:1 and 1:40:1 at a substrate temperature of 100 °C for GaAs and InP, respectively. Such rate enhancements were found to be typical with these materials. Bromine ion-beam-assisted etching also appears to have an advantage over chlorine ion-beam-assisted etching in that high anisotropy can be achieved with bromine in both the GaAs and the InP materials systems at substrate temperatures as high as 200 °C as compared to chlorine where the etching of GaAs is spontaneous and isotropic at temperatures above 150 °C. © 1998 American Vacuum Society.