A fin-shaped field effect transistor includes a substrate and a gate. The substrate includes an active area, where the active area includes a fin structure having at least an extension part protruding from the fin structure. The gate is disposed over the fin structure and directly on the extension part. The present invention also provides a planar field effect transistor including a substrate and a gate. The substrate includes an active area, where the active area includes a frame area and a penetrating area penetrating through the frame area. The gate is disposed over the active area, where the gate is directly disposed on the penetrating area, and the frame area at least at a side of the gate constitutes a source/drain surrounding an isolation island.