A semiconductor device includes a substrate in which a cell region and contact regions located at both sides of the cell region are defined, a first source layer formed over the substrate, a second source layer formed over the first source layer, a reinforcement pattern formed in the second source layer, a stacked structure including conductive layers and insulating layers alternately stacked over the second source layer and the reinforcement pattern, channel layers passing through the stacked structure and the second source layer and electrically coupled to the second source layer, and an isolation insulating pattern passing through at least one top conductive layer of the conductive layers.