A transistor including a gate, an active stacked structure, a dielectric layer, a source and a drain. The gate is located over a first surface of the dielectric layer. The active stacked structure, including a first active layer and a second active layer, is located over a second surface of the dielectric layer. The source and the drain are located over the second surface of the dielectric layer and at two sides of the active stacked structure and extend between the first active layer and the second active layer of the active stacked structure.