An SiC semiconductor device and a related manufacturing method are disclosed having a structure provided with a p+-type deep layer formed in a depth equal to or greater than that of a trench to cause a depletion layer between at a PN junction between the p+-type deep layer and an n−-type drift layer to extend into the n−-type drift layer in a remarkable length, making it difficult for a high voltage, resulting from an adverse affect arising from a drain voltage, to enter a gate oxide film. This results in a capability of minimizing an electric field concentration in the gate oxide film, i.e., an electric field concentration occurring at the gate oxide film at a bottom wall of the trench.