Photonic crystals have received growing interest over the past decade on account of their excellent functionality to guiding and manipulating electromagnetic radiation and their diverse applications. Our approach to fabricate crystals is by a two step etching process in a semiconductor hetero-structure of gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) grown using molecular beam epitaxy (MBE). An array of holes was dry etched in Cl2/Ar inductively coupled plasma. Etching selectivity between the mask and the substrate was 10:1.2 By using SF6 in addition to the boron-tri-chloride (BCl3) chemistry, the GaAs is etched selectively over the AlGaAs with selectivities over 5:1. Thus a robust two-step etching process has been developed based entirely on dry etching© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.