Semiconductor devices and method of manufacturing the same

A semiconductor device, comprising:

• gate electrodes on a substrate and spaced apart from each other;
• a channel structure penetrating the gate electrodes, the channel structure including a channel layer, a gate dielectric layer between the channel layer and the gate electrodes, and a channel pad facing and contacting the channel layer;
• string select gate electrodes on the gate electrodes and the channel structure;
• and
• a string select channel structure penetrating the string select gate electrodes, the string select channel structure including a string select channel layer in contact with the channel pad, a string select gate dielectric layer between the string select channel layer and the string select gate electrodes, and a string select channel pad facing and contacting the string select channel layer,
• wherein at least one of the channel pad and the string select channel pad includes a lower portion and an upper portion expanded in a horizontal direction on the lower portion.

A semiconductor device, comprising:

• a substrate;
• a stack structure on the substrate, the stack structure including interlayer insulating layers and gate electrodes alternately stacked on the substrate;
• a channel structure penetrating the stack structure, the channel structure including a channel layer, a gate dielectric layer between the channel layer and the gate electrodes, and a channel pad facing and contacting the channel layer;
• a first insulating layer on the stack structure, the first insulating layer covering an upper portion of the channel structure;
• a second insulating layer on the first insulating layer, the second insulating layer covering the channel pad of the channel structure;
• an upper stack structure on the second insulating layer, the upper stack structure including upper interlayer insulating layers and upper gate electrodes alternately stacked on the second insulating layer;
• and
• a string select channel structure penetrating the upper stack structure and contacting the channel structure, a lower portion of the string select channel structure having a width smaller than a width of an upper portion of the channel structure,
• wherein the channel pad includes an expanded portion extending in a horizontal direction on the gate dielectric layer.