Semiconductor device and manufacturing method thereof

A semiconductor device includes a first n− type layer and a second n− type layer that are sequentially disposed on a first surface of an n+ type silicon carbide substrate; a first trench and a second trench that are disposed at the second n− type layer and are spaced apart from each other; a p type region surrounding a lateral surface and a lower surface of the first trench; an n+ type region disposed on the p type region and the second n− type layer; a gate insulating layer disposed in the second trench; a gate electrode disposed on the gate insulating layer; an oxide layer disposed on the gate electrode; a source electrode disposed on the oxide layer and the n+ type region disposed in the first trench; and a drain electrode disposed at a second surface of the n+ type silicon carbide substrate.