A double-gate semiconductor device includes a substrate, an insulating layer, a fin and a gate. The insulating layer is formed on the substrate and the gate is formed on the insulating layer. The fin has a number of side surfaces, a top surface and a bottom surface. The bottom surface and at least a portion of the side surfaces of the fin are surrounded by the gate. The gate material surrounding the fin has a U-shaped cross-section at a channel region of the semiconductor device.