In a SiC bipolar semiconductor device with a mesa structure having a SiC drift layer of a first conductive type and a SiC carrier injection layer of a second conductive type that are SiC epitaxial layers grown from a surface of a SiC single crystal substrate, the formation of stacking faults and the expansion of the area thereof are prevented and thereby the increase in forward voltage is prevented. Further, a characteristic of withstand voltage in a reverse biasing is improved. An forward-operation degradation preventing layer is formed on a mesa wall or on a mesa wall and a mesa periphery to separate spatially the surface of the mesa wall from a pn-junction interface. In one embodiment, the forward-operation degradation preventing layer is composed of a silicon carbide low resistance layer of a second conductive type that is equipotential during the application of a reverse voltage. In another embodiment, the forward-operation degradation preventing layer is composed of a silicon carbide conductive layer of a second conductive type, and a metal layer that is equipotential during the application of a reverse voltage is formed on a surface of the silicon carbide conductive layer. In still another embodiment, the forward-operation degradation preventing layer is composed of a high resistance amorphous layer.