Significantly higher electron mobilities compared to silicon make III-V compound semiconductors the materials of choice for high speed, low power devices. The poor quality of thermal oxide layers grown on these surfaces, however, has limited the use of III-V materials in microelectronics. Recent advances in depositing high-k films on silicon using atomic layer deposition (ALD) could expand the use of III-V materials in high volume manufacturing. ALD offers precise control of film thickness, low processing temperatures, and excellent conformality on high aspect ratio structures. ALD relies on self-terminating chemisorption of a reactant on a surface producing up to a monolayer coverage. Recent results show improved gate stack quality in the absence of interfacial layers that are formed typically by reoxidation after cleaning or by reaction during high-k deposition. Controlled removal of the native oxide and passivation/activation of the surface prior to depositing high dielectric constant materials are important process to develop and understand. Etching techniques to remove native oxides on III-V compounds such as liquid phase chemical etching, thermal desorption, and ion bombardment face issues of partial oxide removal, roughened surfaces, and selective etching, which can produce changes in surface stoichiometry. Gas phase processing provides an alternative etching technology that not only addresses the issues of process repeatability and uniformity, but also reduces environmental impact and thermal budget by minimizing the use of ultra pure water and reducing the necessity for recleaning. This study investigated gas phase etching of In-based III-V materials using mixtures of anhydrous HF and water vapor at a total pressure of 100 Torr and a temperature of 29ûC. Native oxide removal and surface termination of InAs(100) and InSb(100) using liquid and gas phase HF chemistries were studied using x-ray photoelectron spectroscopy. Aqueous HF etching removed the native oxides on InAs and produced elemental As, which reoxidized when exposed to air. On InSb the native oxides were not completely removed due to F-termination, which passivated the surface. Gas phase HF etching of InSb native oxide completely removed Sb₂O₅ producing a stoichiometric semiconductor surface terminated by F atoms on primarily In sur- face sites. On InAs gas phase HF completely removed As₂O₃ producing two surface stoichiometries. For the majority of HF to water molar ratios studied, a stoichiometric bulk metal and an As-rich overlayer was produced. For a lean HF composition, an As-rich bulk metal and In-rich overlayer was produced. Deposition of Al₂O₃ by atomic layer deposition (ALD) at 170°C directly onto F-terminated InSb produced a chemically sharp Al₂O₃/InSb interface. ALD of Al₂O₃ on an In-rich overlayer on InAs resulted in an interfacial layer containing As-oxide.