The key technology for a UV sensor is forming a very shallow pn junction and ohmic contacts at this junction. A 6H-SiC UV sensor with high responsivity was realized by introducing nitrogen implantation and lowering the annealing temperature of Ni/SiC for ohmic contacts under N-2 gas. The junction depth of this UV sensor was about 0.1 mum and the responsivity was 187.6 mA/W with a wave length of 290 nm at room temperature. We succeeded in operating this sensor at 700 degreesC.