A selective reactive ion etching process which etches InP and InGaAs, but not InAlAs, using a mixture of SiCl4/SiF4/HBr gases has been developed. Optical emission spectroscopy shows that the dominant emitting species in the plasma are HBr+, Br, and Br2, with a weaker emission from SiBr and SiHBr. We believe that the bromosilanes or chlorosilanes of the form (SiHxBry,SiHxCly) are responsible for the etching of these In‐containing compounds by the formation of indium bromosilanes and indium chlorosilanes. Using a flow rate ratio of SiCl4/HBr of 7/15 sccm, a pressure of 100 mTorr and with dc bias of 80 V, an etch rate of InGaAs and InAlAs as high as 100 nm/min at room temperature was achieved with good surface morphology. The addition of SiF4suppresses the etching of InAlAs and the selectivity obtained can be changed by varying the proportion of SiF4. At a flow rate ratio (SiCl4:SiF4:HBr) of 5/6/20 sccm, dc bias of ≤70 V and a pressure of 150 mTorr, the selectivity obtained is extraordinarily high (≳600:1) for this material system. ©1995 American Institute of Physics.