A method for fabricating semiconductor device includes the steps of: providing a substrate having a cell region and a peripheral region; forming a bit line structure on the cell region and a gate structure on the peripheral region; forming an interlayer dielectric (ILD) layer around the bit line structure and the gate structure; forming a conductive layer on the bit line structure; performing a first photo-etching process to remove part of the conductive layer for forming storage contacts adjacent two sides of the bit line structure and contact plugs adjacent to two sides of the gate structure; forming a first cap layer on the cell region and the peripheral region to cover the bit line structure and the gate structure; and performing a second photo-etching process to remove part of the first cap layer on the cell region.