In situ anti-oxidation treatment after the growth of GaAs is essential for an ideal interface between GaAs and an Al2O3 gate dielectric, because the arsenic oxide is a major origin of interface states. The growth of AlP epitaxial layer on the top of GaAs was proposed as a novel anti-oxidation passivation method. The AlP layer almost converted to Al2O3 upon air exposure, serving as both a stable anti-oxidation layer and as part of a gate dielectric. Compared with surface passivation with Al by exposure to TMAl (trimethylaluminum), which we have proposed previously, the morphology of the passivated surface, which is a critical factor for the performance of a metal-insulator-semiconductor (MIS) structure, was dramatically improved due to the coexistence of a group-V precursor. For an ideal interface without arsenic oxide, an arsenic-free surface prior to the AlP growth was also required. H2S treatment allowed us to obtain the low-As-content c(8 x 2) surface reconstruction of GaAs for the first time by MOVPE. Passivation by AlP on the low-As-content c(8 x 2) surface reconstruction of GaAs has made it possible to obtain an Al2O3/GaAs gate stack which exhibited smooth morphology and complete suppression of arsenic oxide. Reduction of interface states by this passivation was evidenced by the improved photoluminescence intensity from GaAs. (C) 2009 Elsevier B.V. All rights reserved.