We demonstrate an in situ surface passivation technique for the formation of high-permittivity gate dielectric on GaAs using a multiple-chamber metallorganic chemical vapor deposition system. Vacuum annealing and SiH4 annealing were performed prior to HfO2 deposition. X-ray photoelectron spectroscopy and transmission electron microscopy results show that the SiH4 surface passivation can effectively suppress the formation of Ga or As oxide during the HfO2 deposition process. TaN/ HfO2/ GaAs metal-oxide-semiconductor ( MOS) capacitors were fabricated. Electrical characteristics show that an equivalent oxide thickness of 2.03 nm and a low leakage current density of 1.55 x 10(-4) A/cm(2) at V-FB- 1 V gate bias as well as excellent thermal stability were achieved with the SiH4 surface passivation. (c) 2007 The Electrochemical Society.