A semiconductor device is provided that has a plurality of Fin structures extending on a substrate along a first direction; a gate stack structure extending on the substrate along a second direction and across the plurality of Fin structures, wherein the gate stack structure comprises a gate conductive layer and a gate insulating layer, and the gate conductive layer is formed by a doped poly-semiconductor; trench regions in the plurality of Fin structures and beneath the gate stack structure; and source/drain regions on the plurality of Fin structures and at both sides of the gate stack structure along the first direction. A method of manufacturing a semiconductor device is also provided.