A semiconductor device includes a magnetic random access memory (MRAM). The MRAM comprises a plurality of MRAM cells including a first type MRAM cell and a second type MRAM cell. Each of the plurality of MRAM cells includes a magnetic tunneling junction (MTJ) layer including a pinned magnetic layer, a tunneling barrier layer and a free magnetic layer. A size of the MTJ film stack of the first type MRAM cell is different from a size of the MTJ film stack of the second type MRAM cell. In one or more of the foregoing and following embodiments, a width of the MTJ film stack of the first type MRAM cell is different from a width of the MTJ film stack of the second type MRAM cell.