Inductively coupled plasma etching of GaAs/AlGaAs was investigated in BCl3/Cl2/Ar using a mixture design experiment. According to the model extracted from the experiment, the etch rate was linearly proportional to the gas flows, and the process was reactant or diffusion limited. Etch rates from 200 to over 3000 nm/min were obtained. Equirate etch was observed for AlGaAs films with different aluminum content in the entire gas composition range. A quadratic dependence was observed for the etch rates of the resist mask with the gas flows. Etched profiles ranged from positively sloped to vertical to negatively sloped depending on the gas composition. Smooth etched surfaces and mirror quality smooth sidewalls were obtained. © 1998 American Vacuum Society.