We report significant improvements in the high-k/In0.53Ga 0.47As interface quality by controlling atomic layer deposition (ALD) oxidizer chemistry. A step-by-step correlation between electrical data and chemical reactions at the high-k/InGaAs interface has been established using synchrotron photoemission. AsOx, GaOx, and In 2O3 formed during unintentional ALD surface oxidation and the increase of As-As bonds are responsible for degrading device quality. A better quality H2O-based high-k gate stack is evidenced by less capacitance-voltage (CV) dispersion (14% in ZrO2), smaller CV hysteresis (37% in Al2O3 and 47% in ZrO2), fewer border traps (Qbr) (96% in Al2O3 and 25% in ZrO2), and lower mean interface traps density (Dit) (91% in Al2O3 and 29% in ZrO2). Improvements in Id and Gm therefore have been achieved by replacing O3 with H2O oxidizer. Our work suggests that H 2O-based high-k is more promising than O3-based high-k. These results positively impact the industry's progress toward III-V CMOS at the 11nm node.