A semiconductor device includes a substrate including a first region and a second region, a bit line structure that extends over the first region and the second region, an upper spacer structure on a first sidewall of the bit line structure on the first region of the substrate, and an insulation spacer structure on the first sidewall of the bit line structure on the second region of the bit line structure. The upper spacer structure may include first, second and third upper spacers sequentially stacked on the sidewall of the bit line structure in a first horizontal direction. The insulation spacer structure may include first, second, third and fourth insulation spacers sequentially stacked on the sidewall of the bit line structure in the first horizontal direction. The first, second and third insulation spacers include substantially the same materials as the first, second and third upper spacers, respectively.