Metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated with amorphous Al2O3 and HfO 2/SiOx-Si gate stacks, grown by molecular beam deposition. As and In oxides were observed at the Al2O3/In0.17 Ga0.83 As interface, whereas no oxides were detected on the Si-passivated In0.17 Ga0.83 As surface after HfO2 deposition. Traces of As were found in both gate stacks. Si-passivated MOSFETs, with a drain current of 2.8× 103 μA/mm at Vg-Vt=2.0 V, Vd=1.0 V, Ion/Ioff =1× 107, and inverse subthreshold slope of 98-120 mV/decade, show superior performance with respect to devices without Si interlayer. © 2010 American Institute of Physics.