A simple Cl-2/Ar plasma chemistry can provide smooth, high-rate etching of InP, InAs, InGaAs, AlInAs, and InGaAsP at room temperature under conditions in which there is a balance between formation and sputter desorption of the normally involatile InCl3. When the neutral/ion ratio is either too high or too low, surface roughening is apparent due either to the presence of InCl3, or to preferential loss of the group V element. The etching has been investigated as a function of microwave power (600-1000 W), rf power (0-300 W), process pressure (1.5-10 mTorr), and Cl-2:Ar ratio under electron cyclotron resonance conditions. Use of N-2 or H-2, rather than Ar, as gas additives to the chlorine, did not produce smooth, stoichiometric etched surfaces.