THREE-DIMENSIONAL (3D) SEMICONDUCTOR MEMORY DEVICE AND ELECTRONIC SYSTEM INCLUDING THE SAME

A 3D semiconductor memory device includes a substrate, a stack structure comprising interlayer dielectric layers and gate electrodes alternately and repeatedly stacked on the substrate, vertical channel structures penetrating the stack structure, a separation structure spaced apart from the vertical channel structures and filling a trench crossing the stack structure, the separation structure comprising a spacer covering an inner sidewall of the trench, and a first conductive contact filling an inner space of the trench surrounded by the spacer, an insulating layer covering the substrate and the stack structure, contact plugs penetrating the insulating layer so as to be connected to the gate electrodes of the stack structure, and a second conductive contact spaced apart from the stack structure and penetrating the insulating layer so as to be connected to a peripheral circuit transistor. A bottom surface of the first conductive contact is at a level lower than a bottom surface of the spacer.