Both Ga-based (GaAs, AlGaAs) and In- based (InGaP, InP, InAs, and InGaAsP) compound semiconductors were etched in a planar inductively coupled plasma (ICP) reactor in pure BCl3. The Ga- based materials etched at significantly higher rates, as expected from the higher volatilities of their trichloride etch products relative to InCl3. In contrast to the more common cylindrical geometry ICP sources, the dc self- bias which controls ion energy is not strongly dependent on source power up to similar to 400 W while etch rates increase rapidly over this power range. The source tunes easily even at very low powers ( < 100 W) but operates inefficiently above &SIM; 10 mTorr, with a marked decrease in both emission intensity from the discharge and in resulting etch rates of the compound semiconductors. The etched surfaces of both AlGaAs and GaAs have comparable root- mean- square roughness and similar stoichiometry to the unetched control samples, while the surfaces of In- based materials are degraded by the BCl3 etching. (C) 2004 The Electrochemical Society.