The present application discloses a semiconductor device and a method for fabricating the semiconductor device. The semiconductor device includes a substrate having plurality of contacts, a plurality of composite plugs positioned above the plurality of contacts, a plurality of metal spacers positioned above the substrate; and a plurality of air gaps positioned above the substrate. At least one of the plurality of composite plugs includes a protection liner having a U-shaped profile and a metal plug in the protection liner, and the protection liner is in direct contact with one of the plurality of contacts.