A FinFET that includes a semiconductor substrate that has insulating areas, a fin structure, a gate dielectric layer, a gate electrode structure, a drain structure and a source structure is provided. The fin structure is disposed to extend on the semiconductor substrate between two insulating areas. The gate dielectric layer is disposed to extend across two sides of the fin structure. The gate electrode structure is disposed on the gate dielectric layer. The drain structure is disposed at a first side of the gate electrode structure and has a first resistance relative to the gate electrode. The source structure is disposed at a second side of the gate electrode structure and has a second resistance relative to the gate electrode. The first resistance is larger than the second resistance.