Abstract: A semiconductor device includes: 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 includes 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.