The present application discloses a method for fabricating a semiconductor device. The method includes providing a substrate; forming an insulating layer above the substrate; forming a first opening in the insulating layer; conformally forming a first framework layer in the first opening; forming an energy-removable layer on the first framework layer and filling the first opening; forming a second opening along the energy-removable layer and the first framework layer; conformally forming a second framework layer in the second opening; forming a top contact on the second framework layer and filling the second opening and forming a top conductive layer on the top contact; and performing an energy treatment to transform the energy-removable layer into porous insulating layers on two sides of the top contact.