Electron cyclotron resonance (ECR) plasma etch processes with CH4/H2/AR have been investigated on different III–Vsemiconductor materials (GaAs, AlGaAs, InGaAs, and InP). The passivation depth as a function of the GaAs carrierconcentration and the recovery upon annealing at different temperatures have been determined by C-V measurements.Little degradation on the characteristics of Schottky diodes is observed with increasing process biases. If the GaAs toplayer of an AlGaAs/GaAs heterostructure is removed by plasma processing the Hall mobility is restored to 74% afterannealing at 425°C. This is compared to a wet chemically etched reference sample. The 2-DEG sheet density fully recovers.However, if an Si -doped layer is incorporated in the heterostructure the Hall mobility and the sheet density completelyrestore after plasma etching and subsequent annealing. In the experiments minimal damage is observed at a substrate biasof –40 V. The direct current and high frequency characteristics of a dry and wet etched pseudomorphic heterostructurefield-effect transistors are compared.