A process for anisotropically etching AlGalnP/GaAs laser structures in a high-temperature (180degC), single-step BCl3/Cl2/Ar plasma process is demonstrated. The etch rate is shown to be stable over the duration of the etch due to its in- sensitivity to temperature. However, this etch process is unsuitable for etching high-aspect-ratio features due to the strong aspect ratio dependence of the GaAs etch rate at 180degC. A two-step etch where the GaAs is etched at 25degC and the AlGalnP layers are etched at 180degC is demonstrated that etches both materials anisotropically. The relative amount of Ar in the plasma has a strong effect on both the sidewall quality and the aspect-ratio-dependent etch rate. Finally, a process to etch anisotropic microstructures with a weak etch rate dependence on aspect ratio is reported.