Reactive ion etching of GaSb and GaAlSb using pure SiCl4 was investigated. Etching rate and etching profiles were characterized as functions of working pressure, chamber background pressure, flow rate, and power density. The etching rate and profile of metal organic chemical vapor deposited-grown GaSb and GaAlSb thin films are strongly dependent on background pressure and applied power. These interesting characteristics can be applied to control selective or nonselective etchings for device fabrication. Etching profiles exhibited a high degree of anisotropy and smooth surface morphologies.