A semiconductor device includes a substrate including a first region and a second region, a first gate dielectric layer, a first lower gate electrode, and a first upper gate electrode sequentially stacked on the first region, a second gate dielectric layer, a second lower gate electrode, and a second upper gate electrode sequentially stacked on the second region, a first spacer disposed on a sidewall of the first upper gate electrode, a second spacer disposed on a sidewall of the second upper gate electrode, a third spacer covering the first spacer on the sidewall of the first upper gate electrode, and a fourth spacer covering the second spacer on the sidewall of the second upper gate electrode. At least one of a first sidewall of the first lower gate electrode and a second sidewall of the first lower gate electrode is in contact with the third spacer.