Laser-assisted etching techniques have been developed for alloyselective patterning of GaAs/AlGaAs layered structures. Such techniques are potentially very important for the fabrication of a large variety of heterostructure devices. Studies have been carried out with several liquid etchants and have utilized a CW dye laser tuned to a wavelength above the band edge of GaAs, but below that of the AlGaAs layer (e.g., λ = 0.85 μm) to etch GaAs. Using the laser focal spot to spatially define the etched area, features exhibiting very smooth interface surfaces were produced in MBE-grown epitaxial layers. A high degree of selectivity for GaAs over A1(0.4)Ga(0.6)As, low background etch rates, and high feature etch rates (> 2 μm/min) were demonstrated. Patterned etching with AZ 1350J photoresist exhibited good pattern resolution and nearly vertical sidewall profiles. Etchant mixtures of dilute H2S04:H202:H20 and HNO3:H20 produced qualitatively different results, with the HNO3:H20 mixture exhibiting a tendency to leave a residual GaAs layer at the interface, even for long etch times. Surface analysis techniques, including Auger spectroscopy, profilometry, and interference contrast microscopy have been used to characterize the etched structures, and a simplified analytical model has been used to predict the qualitative dependence of etch rate on layer thickness.