A semiconductor device includes a first conductive pattern at an upper portion of a first insulating interlayer on a first substrate, a first plurality of conductive nanotubes (CNTs) extending vertically, a second conductive pattern at a lower portion of a second insulating interlayer beneath a second substrate, and a second plurality of CNTs extending vertically. A lower surface of the second insulating interlayer contacts an upper surface of the first insulating interlayer. At least a portion of a sidewall of each of the first plurality of CNTs is covered by the first conductive pattern, and at least a portion of a sidewall of each of the second plurality of CNTs is covered by the second conductive pattern. The first and second conductive patterns vertically face each other, and at least one of the first plurality of CNTs and at least one of the second plurality of CNTs contact each other.