A vertical semiconductor device includes: a channel on a substrate, the channel extending in a first direction substantially perpendicular to an upper surface of the substrate; a first data storage structure contacting a first sidewall of the channel; a second data storage structure on a second sidewall of the channel; and gate patterns on a surface of the second data storage structure, wherein the gate patterns are spaced apart from each other in the first direction, and the gate patterns extend in a second direction substantially parallel to the upper surface of the substrate.