A memory device may include a plurality of semiconductor patterns on a substrate including a plurality of first impurity regions doped at a first impurity concentration, a plurality of second impurity regions at portions of the substrate contacting the plurality of semiconductor patterns and doped at a second impurity concentration, a plurality of channel patterns on the plurality of semiconductor patterns, a plurality of gate structures, a plurality of third impurity regions at portions of the substrate adjacent to end portions of the plurality of gate structures, and a plurality of fourth impurity regions at portions of the substrate between the second and third impurity regions and between adjacent second impurity regions. The plurality of fourth impurity regions may be doped at a third impurity concentration which may be lower than the first and second impurity concentrations.