BCl3 reactive ion etching for gate recessing of GaInP/InGaAs/GaAs pseudomorphic high electron mobility transistors (PHEMTs) is found improved by the addition of an appropriate amount of Ar to the gas flow. The influence of the BCl3/Ar gas flow ratio on GaAs to GaInP etch selectivity, surface roughness, and surface damage was studied. The results indicate that the conditions for minimum plasma damage, as determined by photoreflectance (PR) spectroscopy, corresponded with the conditions for minimum surface roughness, as determined by atomic force microscopy (AFM). The optimal BCl3/Ar gas flow ratio for minimum surface damage and roughness was found to be 6:4. Two BCl3:Ar flow rate ratios, 6:4 (optimal ratio) and 10:0 (pure BCl3) were used for gate recess etching in the fabrication of GaInP/InGaAs/GaAs PHEMTs. From drain–source current to gate–source voltage (Ids–Vgs) measurements, it was found that the plasma-induced damage for the sample Sc dry etched with 6:4 BCl3/Ar is less than that of the sample Se dry etched with pure BCl3. The dc and small signal rf characteristics of PHEMT Sc were superior to those of the wet-etched PHEMT S0 and PHEMT Se dry etched with pure BCl3. The improvement is attributed to the lower parasitic source resistance associated with- - the tighter recess geometry of the BCl3 plasma recess device. These results show that photoreflectance spectroscopy is a powerful tool for investigating surface damage and can be used to improve the performance of PHEMTs. © 1998 American Vacuum Society.