The authors have investigated chlorine based inductively coupled plasma etching of GaN by using different gas mixtures of Ar, Cl-2, and N-2. The etch mechanism and N-2 role have been studied. We found that both ion energy and ion current density are important. The N-2 plays a multiple role in etching GaN, chemical reaction, and ion bombardment. A reliable process to fabricate GaN nanophotonic crystals has been developed. Plasma conditions have been optimized toward a balance of ion current density, ion energy, and chemical species density. As a result, flat bottom, anisotropic photonic crystal with a=215 nm d=129 nm has been fabricated at an etch rate of 320 nm/min and an etch depth of 650 nm. For comparison, an etch rate of 530 nm/min has been obtained in etching trench lines down to 1.61 mu m deep with a width of 500 nm. The developed process has been used to fabricate GaN photonic crystal (PC) waveguides for 1.55 mu m wavelength. Transmission measurements reveal the Gamma M stop band in hole type PC and illustrate the feasibility of the fabrication process. (C) 2007 American Vacuum Society.