Disclosed are a semiconductor device and a manufacturing method thereof. According to the semiconductor device and the manufacturing method thereof according to exemplary embodiments of the present invention, after the dopant source layer is uniformly deposited on a channel layer of the device with the 3-dimensional vertical structure by the plasma-enhanced atomic layer deposition (PEALD) method, the deposited dopant source layer is heat-treated so that the dopants are diffused into the channel layer to function as charge carriers, thereby preventing the charges in the channel layer from being reduced. According to the exemplary embodiments of the present invention, the diffusion speed and concentration of the dopant may be controlled by forming the barrier layer between the channel layer and the dopant source layer.