A method for fabricating semiconductor device includes the steps of forming an inter-metal dielectric (IMD) layer on a substrate, forming a trench in the IMD layer, forming a synthetic antiferromagnetic (SAF) layer in the trench, forming a metal layer on the SAF layer, planarizing the metal layer and the SAF layer to form a metal interconnection, and forming a magnetic tunneling junction (MTJ) on the metal interconnection.