The present application discloses provides a method for fabricating a semiconductor device. The method includes providing a substrate, forming a sacrificial structure above the substrate, forming a supporting liner covering the sacrificial structure, forming an energy-removable layer covering the supporting liner, performing a planarization process until a top surface of the sacrificial structure is exposed, performing an etch process to remove the sacrificial structure and concurrently form a first opening in the energy-removable layer, forming covering liners on sidewalls of the first opening and on a top surface of the energy-removable layer, forming a first conductive feature in the first opening, and applying an energy source to turn the energy-removable layer into a porous insulating layer.