A new selective reactive ion etching (RIE) process has been developed for etching InGaAs and InP over InAIAs using a mixture of SiCl4/SiF4/HBr gases. Optical emission spectroscopic (OES) investigation showed that the dominant emitting species in the plasma are HBr+. Br, and Br-2, with weaker emission from SiBr and SiHBr. Using a flow rate of SiCl4/HBr of 6/15 SCCM, a pressure of 100 mTorr, and with a de bias of 180 V, the etch rates of InGaAs and AlInAs can be as high as 200 nm/min at room temperature with good surface morphology. The formation of bromosilanes or chlorosilanes of the form (SiHxBry, SiHxCly) in the plasma is believed to be responsible for the etching In-containing compounds through the formation of indiumbromosilanes and indiumchlorosilanes. The selectivity of etching InGaAs and InP over InAlAs is obtained by the addition of SiF4 to the mixture of SiCl4/HBr, which is thought to be due to the formation of an etch stop layer of AlF3 on the AlInAs layer. Using a flow rate ratio of SiCl4/SiF4/HBr of 5/6/25 SCCM, a de bias of less than or equal to 70 V, and a pressure of 100 mTorr, the selectivity was extraordinary high for this material system a minimum of (600:1). The etching was stopped on a 5-nm-thick AllnAs layer for at least 60 min. These values of selectivity are an order of magnitude higher than the reported values in the literature. Moreover, this RIE process (SiC4/SiF4/HBr) etches silicon nitride, and NiCr very slowly. Structures in InP have been etched as deep as 6 mu m with very little erosion to the mask which was a very thin layer (100 nm thick) of either Si3N4 or NiCr. The dry etch damage was evaluated using Hall effect measurements made on a high electron mobility transistors material structure. This structure had a 7 nm InGaAs capping layer. Etching the 7 nm cap layer had very little effect on the Value of the sheet carrier concentration acid the mobility even after 7 min of continuous bombardment of the active layers by selective etching of the 7 nm capping layer.