A semiconductor device includes a memory cell region including memory cells arranged along channel holes, the channel holes being provided on a substrate to extend in a direction perpendicular to an upper surface of the substrate, and a peripheral circuit region disposed outside of the memory cell region and including low voltage transistors and high voltage transistors. The low voltage transistors include first transistors including a first gate dielectric layer and a first gate electrode layer including a metal, and the high voltage transistors include second transistors including a second gate dielectric layer having a dielectric constant lower than a dielectric constant of the first gate dielectric layer, and a second gate electrode layer including polysilicon.