A method for fabricating semiconductor device includes the steps of: forming a first bit line structure on a substrate; forming a first spacer adjacent to the first bit line structure; forming an interlayer dielectric (ILD) layer adjacent to the first spacer; removing part of the ILD layer and part of the first spacer to expose a sidewall of the first bit line structure; and forming a first storage node contact isolation structure adjacent to the first bit line structure, wherein the first storage node contact isolation structure contacts the first bit line structure and the first spacer directly.