SEMICONDUCTOR DEVICES AND DATA STORAGE SYSTEMS INCLUDING THE SAME

A semiconductor memory device includes: a first semiconductor structure including a first substrate, circuit devices on the first substrate, and a lower interconnection structure connected to the circuit devices; and a second semiconductor structure on the first semiconductor structure. The second semiconductor structure may include: a second substrate having a first region and a second region; a substrate insulating layer extending through the second substrate; a landing pad extending through the substrate insulating layer; gate electrodes spaced apart from each other and stacked on the first region in a first direction and extending with different lengths in a second direction on the second region, each of the gate electrodes including a gate pad region on the second region having an exposed upper surface; and a gate contact plug extending through the gate pad region of at least one of the gate electrodes and into the landing pad. The landing pad may include a pad portion that is surrounded by an internal side surface of the substrate insulating layer, and a via portion extending from the pad portion to the lower interconnection structure.