Dry etching characteristics of GaN using reactive ion beam etching (RIBE) were studied. Etching profile, etching rate and etching selectivity to a photoresist (PR) mask were investigated as a function of various etching parameters. Characteristics of chemically assisted reactive ion beam etching (CARIBE) and RIBE were compared at varied mixtures of CH4 and Cl2. A highly anisotropie etching profile with a smooth surface was obtained for tilted RIBE with Ch at room temperature. Etching selectivity to a PR was dramatically improved in RIBE and CARIBE when a volume fraction of CH4 to the mixture of CH4 and Ch was larger than 0.83.