The invention provides a semiconductor device and a manufacturing method thereof. The semiconductor device comprises an N-type substrate and an epitaxial layer arranged at the surface of the N-type substrate, wherein the epitaxial layer comprises a groove, a metal layer covering the surface of the groove, an insulation layer covering the surface of the epitaxial layer except the groove, and a first P-type well region which is arranged within the surface of the epitaxial layer and surrounds the groove, the first P-type well region separates the metal layer from the epitaxial layer, and the first P-type well region and a contact region of the metal layer realize ohmic contact. According to the semiconductor device and the manufacturing method thereof, a reverse direction leakage current of the device can be effectively reduced.