Design of thermal oxidation processes has a crucial role to control the metal-oxide-semiconductor (MOS) interface characteristics of 4H-SiC The effects of the oxidant species, i.e. O-2 or H2O on MOS interface properties on both 4H-SiC (0001) Si-face and (000-1) C-face were systematically investigated from the viewpoints of SiO2 growth kinetics and near-interface oxide microscopic structures, as well as those of electrical characteristics of MOS capacitors. As the possible origins of the significantly different MOS electrical properties between dry and wet-oxidized interfaces, the differences in the interface reaction mechanisms to grow SiO2 and those in the strained structure of near-interface SiO2 are indicated. The requirement for the control of O-2:H2O ratio in the oxidizing ambient to optimize the MOS characteristics was also investigated. (C) 2017 Elsevier B.V. All rights reserved.