SEMICONDUCTOR MEMORY DEVICE AND MANUFACTURING METHOD OF THE SEMICONDUCTOR MEMORY DEVICE

A semiconductor memory device, and a method of manufacturing the semiconductor memory device, includes: a substrate including a peripheral circuit, a gate stack structure disposed over the substrate and including a cell array region and a stepped region that extends from the cell array region, a channel structure passing through the cell array region of the gate stack structure, a memory layer surrounding a sidewall of the channel structure, a first contact plug passing through the stepped region of the gate stack structure, and an insulating structure surrounding a sidewall of the first contact plug to insulate the first contact plug from the gate stack structure.