The channel structure CH may have a form in which the lower channel structures CHL of the lower stack structure GS1 and the upper channel structures CHU of the upper stack structure GS2 are connected, and may have a bent portion due to a difference in width in a region in which the connection is performed. A channel layer 140 and a channel embedded insulating layer 150 may be connected to each other between each of the lower channel structures CHL and each of the upper channel structures CHU. A channel pad 155 may be disposed only on each of the upper channel structures CHU. In some example embodiments, the lower channel structure CHL and the upper channel structure CHU may include the channel pad 155, respectively. In this case, the channel pad 155 of each of the lower channel structure CHL may be connected to the channel layer 140 of each of the upper channel structure CHU. An upper interlayer insulating layer 125 having a relatively thick thickness may be disposed in an uppermost portion of the lower stack structure GS1. Shapes of interlayer insulating layers 120 and a shape of the upper interlayer insulating layer 125 may be variously changed in some example embodiments.

Vertical structures VS are illustrated in a form connected without a difference in width in a region in which the lower stack structure GS1 and the upper stack structure GS2 are connected, but the present inventive concepts is not limited thereto. In some example embodiments, similarly to the channel structure CH, the vertical structures VS may have a bent portion due to a difference in width.

For other configurations, the description described above with reference to FIGS. 1 to 3 may be equally applied.