Semiconductor devices include an intrinsic semiconductor region on a substrate, a source region adjacent to a first side surface of the semiconductor region and doped with a p-type dopant, a drain region adjacent to a second side surface of the semiconductor region, a gate electrode on the semiconductor region, a source gate electrode on the source region, and a drain gate electrode on the drain region. The second side surface is a reverse side of the first side surface. The drain region is doped with a p-type dopant.