A semiconductor device may include a substrate, a first doped region and a second doped region on the substrate, a base region on the first doped region, a channel region on the second doped region, and a third doped region and a fourth doped region on the base region and the channel region, respectively. The first doped region and the second doped region may be isolated from direct contact with each other in a first direction that is substantially parallel to a top surface of the substrate. A channel gate structure may be on a side surface of the channel region. A thickness of the base region, in a second direction that is substantially perpendicular to the top surface of the substrate, may be equal to or larger than a thickness of the channel region.