A method for fabricating semiconductor device is disclosed. The method includes the steps of: providing a substrate having a first dielectric layer and a second dielectric layer thereon; forming a drain layer in the first dielectric layer and the second dielectric layer; forming a gate layer on the second dielectric layer; forming a channel layer in the gate layer; forming a third dielectric layer and a fourth dielectric layer on the gate layer and the channel layer; and forming a source layer in the third dielectric layer and the fourth dielectric layer.