Etching selectivity of citric acid buffer based etchant was investigated for the gate recess process of a double delta doped Al0.25Ga0.75As/In0.2Ga0.8As/Al0.25Ga0.75As based pseudomorphic high electron mobility transistor epitaxial layer structure grown by molecular beam epitaxy. Optimization of the etchant resulted in a selectivity of as high as 4800 for GaAs over Al0.25Ga0.75As layer. Source-drain current Id,, during the gate recess was found to be stable for as long as 1200 s. The gate recess undercut was found to increase laterally as a function of recess time. The pH value of the selective etchant played a major role in the enhancement of the selectivity for wet etching of GaAs on Al0.25Ga0.75As. Morphology of the wet etched GaAs/Al0.25Ga0.75As surface was investigated using atomic force microscopy. The observed surface morphology was excellent, with a rms surface roughness value of about 1 nm. X-ray photoelectron spectroscopy analysis indicated the formation of Al2O3 at the wet etched surface of Al0.25Ga0.75As. The etch rate of doped GaAs for this etchant was 40 Angstrom/s. (C) 2004 American Vacuum Society.