The dry etch characteristics of InGaP in BCl3 Planar inductively coupled plasmas (ICP) with additions of Ar or Ne were determined. The inert gas additive provided enhanced etch rates relative to pure BCl3 and Ne addition in particular produced much higher etch rates at low ratios of BCl3 in the mixture. The etched features tended to have sloped sidewalls and much rougher surfaces than for GaAs and AlGaAs etched under the same conditions. The practical effect of the Ar or Ne addition was the ability to operate the ICP source over a somewhat broader range of pressures and still maintain practical etch rates. The use of room temperature BCl3-based etching in a planar ICP appears feasible for base and emitter mesa applications in InGaP/GaAs heterojunction bipolar transistors. (C) 2003 Elsevier Ltd. All rights reserved.