Disclosed is a semiconductor device. The semiconductor device includes a first gate formed in a trench of a semiconductor substrate, a first gate oxide layer on the semiconductor substrate including the first gate, a first epitaxial layer on the first gate oxide layer, first source and drain regions in the first epitaxial layer at sides of the first gate, an insulating layer on the first epitaxial layer, a second epitaxial layer on the insulating layer, a second gate oxide layer on the second epitaxial layer, a second gate on the second gate oxide layer, and second source and drain regions in the second epitaxial layer below sides of the second gate.