The influence of proton irradiation on current–voltage characteristics, N d– N a values and parameters of deep centres in 6H-SiC pn junctions has been studied. The irradiation was carried out with 8-MeV protons with doses from 10 14 to 10 16 cm −2. Irradiation with a dose of 5.4×10 15 cm −2 resulted in a very high resistance of forward-biased pn structures, remaining high even after anneling to 500°C. It is suggested that proton irradiation reduces the holes lifetime and increases the concentration of deep centers, which leads to formation of an i-layer.