An extensive investigation has been performed on inductively coupled plasma etching of InP. Animportant motivation for this work is the fabrication of high-aspect-ratio holes for photonic crystals.The essential chemistry is based on Cl2 with the addition of N2 or O2 for sidewall passivation. Theinfluence of different process parameters such as gas flows, temperature, pressure, ion energy, andinductively coupled plasma power on the hole geometry is presented. It is concluded that photoniccrystals can be etched with Cl2 only; however, temperature and pressure control is critical. Addingpassivation gases largely broadens the window in the parameter space for hole etching. Mostimportantly, etching of narrow holes can be carried out at higher temperatures where the etching ismass limited and spontaneous etching of InP by Cl2 occurs.