GaInAs, InP, and GaAs are etched in a Cl-2/Ar plasma generated by an electron cyclotron resonance source. Analysis using scanning electron microscopy shows no difference in GalnAs surface morphology before or after etching in a Cl-2/Ar plasma. However, a significant increase in the mean surface roughness of GaInAs from 0.2 to 1.9 nm after etching is detected by atomic force microscopy. The mean surface roughness of GaAs also increases from 0.2 to 1.0 nm after etching. X-ray photoelectron spectroscopy was used to measure atomic concentrations on the etched surface. The results show that the increased roughness of etched GalnAs is related to residual etch products that consist of O and Cl. Using atomic force microscopy, the mean surface roughness was measured to be 1.8 nm at 0.5 mTorr and it increased to 2.7 fim at 5 mTorr. The degradation in GaInAs surface morphology with increasing pressure caused an increase in the specific contact resistivity. Etching related roughness can be minimized by using high radio-frequency power, low pressure, and low Cl-2% in Ar. Increasing the ion density by increasing the microwave power allows InP to be etched at 2.7 mu m/min with a Cl-2/Ar plasma at 30 degrees C. A smooth surface obtained at 500 W microwave power has a mean surface roughness of 1.7 nm and the InP stoichiometry remains nearly constant after etching. For a lower microwave power of 100 W, the mean surface roughness increases to 4.3 nm, and the surface is characterized by large islands. An H2O rinse immediately following the etch is able to remove residual etch products as indicated by a decrease in the surface roughness as well as the Cl and O concentrations on the surface.