Semiconductor devices and method of manufacturing the same

A semiconductor device, comprising:

• a substrate;
• a plurality of gate electrodes on the substrate, the plurality of gate electrodes extending in a first direction parallel to an upper surface of the substrate and alternately arranged with an interlayer insulating layer in a second direction perpendicular to the upper surface of the substrate;
• a vertical channel layer on a sidewall of a vertical channel hole extending in the second direction by penetrating through the plurality of gate electrodes and the interlayer insulating layer, wherein a part of the vertical channel layer has a non-uniform thickness at a first vertical level corresponding to the upper surface of the substrate;
• and
• a first gap-fill insulating layer in the vertical channel hole and including an outer wall contacting the vertical channel layer and an inner wall opposite the outer wall, wherein the first gap-fill insulating layer has a non-uniform thickness at the first vertical level.

A semiconductor device, comprising:

• a substrate;
• a plurality of gate electrodes on the substrate, the plurality of gate electrodes extending in a first direction parallel to an upper surface of the substrate and alternately arranged with an interlayer insulating layer in a second direction perpendicular to the upper surface of the substrate;
• a vertical channel layer on a sidewall of a vertical channel hole extending in the second direction by penetrating through the plurality of gate electrodes and the interlayer insulating layer, and in contact with the upper surface of the substrate;
• and
• a first gap-fill insulating layer in the vertical channel hole, the first gap-fill insulating layer being an oxide of the vertical channel layer.