We compared SiO2/SiC interface characteristics for three different oxidation processes (dry-oxygen, water-containing oxygen and water-containing nitrogen atmospheres). Metal-oxide-semiconductor (MOS) structures were fabricated on 8° off-axis 4H-SiC(0001) n- and p-type epitaxial wafers. Electrical characteristics were obtained by I–V measurements, high-frequency capacitance–voltage (C–V) and ac conductance (G–V and G–ω) methods. The samples were also characterized by x-ray photoelectron spectroscopy. Results evidence a remarkable difference between n- and p-type doped samples. The p-type samples showed effective oxide charge density up to three orders of magnitude higher than n-type. This fact was explained by the capturing of majority carriers in near interface oxide traps.