The use of an Ar ion beam and hydrogen chloride gas in the chemically assisted ion beam etching of GaN grown by metalorganic chemical vapor deposition is reported. Etch rates were investigated as a function of ion beam energy and substrate temperature. Hydrogen chloride gas was found to produce higher etch rates at lower ion beam energies (300 eV) and lower rates at higher energies (600 eV) in comparison to Cl2. Highly anisotropic etch profiles are demonstrated that indicate that the process may be suitable for the fabrication of laser facets and mirrors. Changes in surface stoichiometry resulting from the etching process were also investigated using Auger electron spectroscopy.