A semiconductor device includes active pillars protruding from a semiconductor substrate and spaced apart from each other in a first direction and a second direction that is perpendicular to the first direction, a word line extending in the first direction between the active pillars, a drain region disposed in an upper portion of each of the active pillars, and a separation pattern provided between the word line and the drain region. A bottom surface of the separation pattern is disposed at a lower level than a bottom surface of the drain region.