In a semiconductor device and a method of forming such a device, the semiconductor device comprises a substrate of semiconductor material extending in a horizontal direction. A plurality of interlayer dielectric layers is provided on the substrate. A plurality of gate patterns is provided, each gate pattern between a neighboring lower interlayer dielectric layer and a neighboring upper interlayer dielectric layer. A vertical channel of semiconductor material extends in a vertical direction through the plurality of interlayer dielectric layers and the plurality of gate patterns, a gate insulating layer between each gate pattern and the vertical channel that insulates the gate pattern from the vertical channel, the vertical channel being in contact with the substrate at a contact region that comprises a semiconducting region.