An experimental technique to reduce the growth of undesirable interface layer in high-k gate dielectrics is reported. Effects of mixing of TiO2 and Ta2O5 in Y2O3 on the interface layer growth are studied in detail. Chemical composition and the interfacial properties of Y2O3 (TiO2 and Ta2O5 mixed) ultra thin films prepared by RF sputtering on S-passivated GaAs are reported. It is shown that the formation of Ga-O bonding at the GaAs surface and As diffusion in the dielectric may effectively be controlled by mixing of TiO2 and Ta2O5. Band gap (E-g) of the mixed (TiO2)(1-x)(Y2O3)(x) and (Ta2O5)(1-x)(Y2O3)(x) high-k gate dielectrics are found to be similar to 5.3 +/- 0.05 and similar to 5.5 +/- 0.05 eV, respectively. The Ta and Ti incorporated Y2O3 [(Ta2O5)(1-x)(Y2O3)(x) and (TiO2)(1-x)(Y2O3)(x)] films on p-GaAs improve metal-oxide-semiconductor (MOS) capacitor characteristics such as interface state density, accumulation capacitance, hysteresis, and leakage current. The leakage current of similar to 2.4x10(-6) A/cm(2) at V-g = V-fb -1V was achieved for (TiO2)(1-x)(Y2O3)(x)/GaAs gate stacks. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.094203jes] All rights reserved.