A semiconductor device includes a substrate, a bit line structure on the substrate, a first contact structure on a sidewall of the bit line structure, a second contact structure on the bit line structure and spaced apart from the first contact structure across the bit line structure, and an insulation pattern between the bit line structure and the first contact structure. The second contact structure covers at least a portion of a top surface of the bit line structure. The insulation pattern comprises a protrusion that protrudes from a sidewall of the insulation pattern that immediately adjacent to the bit line structure. The protrusion protrudes in a first direction parallel to a top surface of the substrate.