A semiconductor device includes a plurality of gate trenches, each of which has first inner walls, which face each other in a first direction which is perpendicular to a second direction in which active regions extend, and second inner walls, which face each other in the second direction in which the active regions extends. An isolation layer contacts a gate insulating layer throughout the entire length of the first inner walls of the gate trenches including from entrance portions of the gate trenches to bottom portions of the gate trenches, and a plurality of channel regions are disposed adjacent to the gate insulating layers in the semiconductor substrate along the second inner walls and the bottom portions of the gate trenches.