Oxidation of 4H-SiC substrates using an electrochemical method was carried out at room temperature. The oxide layers with a thickness of 1 mum were formed for 5 minutes, 100 times faster than a conventional thermal oxidation method. The oxide thickness with the oxidation time follows the general relationship used for the thermal oxidation of SiC. The oxide layer was found to be SiO2 with carbon by the analysis with XPS. The concentration of carbon in the oxide layers could be reduced to 50% by the thermal annealing at 800degreesC for 30 minutes in H-2/Ar.