A semiconductor device and manufacturing method includes a well structure, a gate stack structure spaced apart from the well structure, the gate stack structure being disposed over the well structure, and a source contact structure facing a sidewall of the gate stack structure. The semiconductor device further includes a channel pattern having pillar parts penetrating the gate stack structure, a first connecting part extending along a bottom surface of the gate stack structure from the pillar parts, and a second connecting part extending from the first connecting part to contact a first surface of the source contact structure facing the well structure.