Oxide traps existing in 4H-SiC MOS capacitors with fast response times that are active in the strong accumulation and depletion regions were characterized by an integrated-charge method. The method is based on the measurement of charging and discharging voltages across MOS capacitors in response to high-frequency voltage pulses. This method can identify traps with response times in the order of hundreds of nanoseconds. The results reveal an increasing density of near-interface traps with energy levels above the bottom of the conduction band, which are the active defects reducing the channel-carrier mobility in 4H-SiC MOSFETs.