An inductively coupled plasma reactive ion etching process was developed for transfer-ring patterns from a thin intermediate mask consisting of Ni or SiNx into GaAs. Smoothed out etch floors and sidewalls can be achieved under an approximately 200 V bias by switching between an anisotropic etch phase and a deposition phase by gas chopping. The deposition of Si-O based film that protects the sidewall from chlorine attack is promoted by the addition of O-2 to an SiCl4/N-2 gas mixture. The total achieved etch depth was approximately 20 mu m in this work, but the process can in principle be adopted for a larger depth and other chlorine-etchable IIIN semiconductors. SiCl4 is shown to act as a suitable deposition gas as well as an etch gas. (c) 2007 American Vacuum Society.