A method for fabricating semiconductor device includes: forming a metal-oxide semiconductor (MOS) transistor on a substrate; forming a first interlayer dielectric (ILD) layer on the MOS transistor; removing part of the first ILD layer to form a trench adjacent to the MOS transistor; forming a trap rich structure in the trench; forming a second ILD layer on the MOS transistor and the trap rich structure; forming a contact plug in the first ILD layer and the second ILD layer and electrically connected to the MOS transistor; and forming a metal interconnection on the second ILD layer and electrically connected to the contact plug.