Disclosed are a semiconductor device and a manufacturing method thereof. The semiconductor device includes source select lines, word lines, drain select lines, and a bit line stacked on a substrate in which a first cell string region and a second cell string region are defined; channel layers and memory layers vertically passing through the source select lines, the word lines, and the drain select lines in each of the first cell string region and the second cell string region; and a common source line vertically passing through the source select lines, the word lines, and the drain select lines at centers of the first cell string region and the second cell string region, and extended to a lower side of the source select lines.