A semiconductor device includes a plurality of blocks on a substrate. Trenches are disposed between the plurality of blocks. Conductive patterns are formed inside the trenches. A lower end of an outermost trench among the trenches is formed at a level higher than a level of a lower end of the trench adjacent to the outermost trench. Each of the blocks includes insulating layers and gate electrodes, which are alternately and repeatedly stacked. Pillars pass through the insulating layers and the gate electrodes along a direction orthogonal to an upper surface of the substrate.