Bipolar degradation is one of the key issues that should be considered in silicon carbide (SiC) MOSFETs. The growth of the highly nitrogen-doped epitaxial layer as recombination-enhancing buffer is well-known practical method for preventing the bipolar degradation. In recent years, the suppression of the stacking fault (SF) expansion into SiC by proton (H+) implantation has been reported. It would be an attractive candidate as a solution for the bipolar degradation, but there are few reports about mechanism of suppression. Thus, in this work, we have investigated the effect of proton implantation on the suppression of SF expansion. We fabricated a vertical SiC-MOSFET which proton was partially implanted into the middle depth of the drift layer by appropriately shielding an active area of the device using silicon pieces. And we performed photoluminescence (PL) inspection after the continuous current stress test for body-diode in SiC-MOSFET. From the shape of expanded SF observed in the PL image after the continuous current stress test, we infer that the proton implanted layer could act as a lifetime killer. And it also suggests the recombination-enhanced buffer at any depth of the drift layer can be introduced by proton implantation. In conclusion, proton implantation would be a promising method for fabricating highly reliable SiC-MOSFETs in the future.