A simple Cl2/Ar plasma chemistry can provide smooth, high‐rate etching of InP, InAs, InGaAs, A1InAs, 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 Cl2:Ar ratio under electron cyclotron resonance conditions. Use of N2or H2, rather than Ar, as gas additives to the chlorine, did not produce smooth, stoichiometric etched surfaces.