Etch rates in excess of 1.5 mu m/min for InP and InSb, 1.2 mu m/min for GaAs and 0.7 mu m/min for GaSb at room temperature were obtained in electron cyclotron resonance IC1/Ar plasmas at low additional rf power (150 W). There was little dependence of etch rate on microwave power over the range 400-1000 W for InP, and selectivities of 6-10 over mask materials such as SiO2, SINx, and W were typical. Smooth surface morphologies were obtained over a wide range of plasma parameters for GaAs and GaSb, while preferential lass of P led to rough morphologies for InP at high rf powers. IC1-based plasmas appear to be promising universal etchants for Ga-and In-based III-V semiconductors.