Semiconductor devices and data storage systems including the same

Abstract

A semiconductor device includes a lower structure including a semiconductor substrate and circuit devices on the semiconductor substrate; a stack structure including interlayer insulating layers and gate electrodes alternating in a vertical direction; and a channel structure penetrating the stack structure. The channel structure includes a core insulating layer, a channel layer, a gate dielectric layer, and a channel pad. A portion of the channel pad overlaps an uppermost gate electrode among the gate electrodes in a horizontal direction. The channel pad includes a first pad layer and a second pad layer on the first pad layer. The second pad layer includes doped polysilicon that is doped with impurities and having N-type conductivity. The first pad layer includes at least one of an undoped polysilicon region and a doped polysilicon region having N-type conductivity and having an impurity concentration lower than an impurity concentration of the second pad layer.