According to example embodiments, a semiconductor device includes a plurality of active pillars protruding from a substrate. Each active pillar includes a channel region between upper and lower doped regions. A contact gate electrode faces the channel region and is connected to a word line. The word line extends in a first direction. A bit line is connected to the lower doped region and extends in a second direction. The semiconductor device further includes a string body connection portion that connects the channel region of at least two adjacent active pillars of the plurality of active pillars.