A semiconductor device includes a substrate having a fin structure, the fin structure having a height in a substantially perpendicular direction to the substrate, and having consecutive upper and lower portions along the height, the lower portion being closer to the substrate than the upper portion. The semiconductor device further includes a gate structure wrapping around a portion of the fin structure, the gate structure having a gate dielectric layer disposed around the fin structure, and a gate electrode layer disposed over the gate dielectric layer. The gate electrode layer includes a first gate metal layer formed along both sides of the lower portion of the fin structure, the first gate metal layer having a first workfunction, and a second gate metal layer formed disposed over the first gate metal layer and wrapped around the upper portion of the fin structure, the second gate metal layer having a second workfunction. The first and the second workfunctions are different.