Thin HfTaOx and HfTaTiOx gate dielectrics (∼7-8 nm) have been rf sputter-deposited on sulfur passivated GaAs. Our experimental results suggest that the formation of Ga-O at GaAs surface and As diffusion in dielectric may be effectively controlled by Ti incorporation. Possibility of tailoring of band alignment via Ti incorporation is shown. Valence band offsets of 2.6 ± 0.05 and 2.68 ±0.05 eV and conduction-band offsets of 1.43 ±0.05 and 1.05 ±0.05 eV were found for HfTaOx (Eg∼5.45 eV) and HfTaTiOx (Eg∼5.15 eV), respectively. 7copy; 2011 American Institute of Physics.