SEMICONDUCTOR MEMORY DEVICES

A semiconductor memory device includes a source layer, a semiconductor layer including a semiconductor protrusion structure, and a drain layer arranged in a first horizontal direction on a substrate, a cell capacitor extending in the first horizontal direction on the substrate and including a lower electrode layer, a capacitor dielectric film, and an upper electrode layer connected to the drain layer, a bit line extending in a vertical direction on the substrate and connected to the source layer, and a gate structure covering the semiconductor protrusion structure and including a gate dielectric film on the semiconductor protrusion structure and a gate electrode film on the gate dielectric film. A value of a first thickness of an end portion of the semiconductor protrusion structure facing the drain layer is greater than a value of a second thickness of another end portion of the semiconductor protrusion structure facing the source layer.