An MRAM device comprises an insulating interlayer comprising a flat first upper surface on a first region and a second region of a substrate. A pattern structure comprising pillar-shaped magnetic tunnel junction (MTJ) structures and a filling layer pattern between the MTJ structures is formed on the insulating interlayer of the first region. The pattern structure comprises a flat second upper surface that is higher than the first upper surface. Bit lines are formed on the pattern structure that contact top surfaces of the MTJ structures. An etch-stop layer is formed on the pattern structure between the bit lines of the first region and the first upper surface of the first insulating interlayer of the second region. A first portion of an upper surface of the etch-stop layer on the first region is higher than a second portion of the upper surface of the etch-stop layer on the second region.