Semiconductor device and method of manufacturing semiconductor device

A semiconductor device comprising:

• a stack including word lines and insulating layers that are alternately stacked;
• first channel layers passing through the stack;
• memory layers enclosing sidewalls of the first channel layers;
• second channel layers disposed on the stack;
• gate insulating layers enclosing sidewalls of the second channel layers;
• third channel layers configured to respectively couple the first channel layers with the second channel layers;
• select lines each comprising a first portion disposed on the stack, and second portions respectively enclosing the second channel layers and protruding into the stack toward the first channel layers;
• and
• a separation insulating structure disposed on the stack and configured to insulate the select lines from each other.

A method of manufacturing a semiconductor device, comprising:

• forming a stack including first material layers and second material layers that are alternately stacked;
• forming a sacrificial layer on the stack;
• forming a separation insulating structure passing through the sacrificial layer and disposed over the first material layers;
• forming a first opening passing through the sacrificial layer, the separation insulating structure, and the stack;
• forming a first channel layer in the first opening;
• forming a sacrificial spacer coupled with the sacrificial layer in the first opening;
• forming in the sacrificial spacer a second channel layer having a width less than a width of the first channel layer;
• and
• forming in the first opening a third channel layer configured to couple the first channel layer with the second channel layer and extend into the second channel layer.