A semiconductor device includes a magnetic tunneling junction (MTJ) on a substrate, a first spacer on one side of the MTJ, and a second spacer on another side of the MTJ, wherein the first spacer and the second spacer are asymmetric. Specifically, the MTJ further includes a first bottom electrode disposed on a metal interconnection, a capping layer on the bottom electrode, and a top electrode on the capping layer, in which a top surface of the first spacer is even with a top surface of the top electrode and a top surface of the second spacer is lower than the top surface of the top electrode and higher than the top surface of the capping layer.