The dry etch selectivity of GaAs over InGaP in BCl3/F-6 discharges with additives of He, Ar, or Xe under Inductively Coupled Plasma conditions was examined. Selectivities over 200 were achieved in BCl3/SF6 or BCl3/SF6/He at low ion energies and moderate ion fluxes. The mechanism for achieving selective etching was studied with Electron Spectroscopy for Chemical Analysis, and is due to formation of non-volatile InClx and InFx reaction products. The key to achieving high selectivity is to minimize sputter-induced desorption of these reaction products. Ion-induced damage in the InGaP was also minimized at low ion energies and moderate ion fluxes.