Semiconductor devices having vertical channel transistors are provided. The semiconductor device includes an insulation layer on a substrate and a buried bit line on the insulation layer. The buried bit line extends in a first direction. An active pillar is disposed on the buried bit line. The active pillar includes a lower dopant region, a channel region having a first sidewall and an upper dopant region vertically stacked on the buried bit line. A contact gate electrode is disposed to be adjacent to the first sidewall of the channel region. A word line is electrically connected to the contact gate electrode. The word line extends in a second direction intersecting the first direction. A string body connector is electrically connected to the channel region. Related methods are also provided.