The dry etch characteristics of GaAs over both AlGaAs and InGaP in planar inductively coupled BCI3-based plasmas(ICP) with additions of SF6 or CF4 were studied. The additions of flourine gases provided enhanced etch selectivities of GaAs/AlGaAs and GaAs/InGaP. The etch stop reaction involving formation of involatile AIF3 and InF3 (boiling points of etch products: AIF3~1300℃, InF3>1200℃ at atmosphere) were found to be effective under high density inductively coupled plasma condition. Decrease of etch rates of all materials was probably due to strong increase of flourine atoms in the discharge, which blocked the surface of the material against chlorine neutral adsorption. The process parameters were ICP source power (0 - 500 W), RF chuck power (0 - 30 W) and variable gas composition. The process results were characterized in terms of etch rate, selectivities of GaAs over AlGaAs and InGaP, surface morphology, surface roughness and residues after etching.