Provided are a semiconductor device and a method for fabricating the same. The semiconductor device can include a transistor structure, including a gate dielectric on a substrate, a gate electrode on the gate dielectric, a spacer at sidewalls of the gate electrode, and source/drain regions in the substrate; and an interlayer dielectric on the transistor structure where an air gap is provided in a region between the spacer, the interlayer dielectric, and the source/drain region of the substrate.