Three-dimensional semiconductor memory device

A three-dimensional (3D) semiconductor memory device comprising:

• a first stack structure block comprising first stack structures arranged side by side in a first direction on a first substrate;
• a second stack structure block comprising second stack structures arranged side by side in the first direction on the first substrate;
• a separation structure disposed on the first substrate between the first stack structure block and the second stack structure block and comprising first mold layers and second mold layers;
• a first contact plug penetrating the separation structure and the first substrate;
• a second contact plug penetrating the separation structure and connected to the first substrate;
• and
• a connection line connecting the first contact plug and the second contact plug.

A three-dimensional (3D) semiconductor memory device comprising:

• a first stack structure block comprising first stack structures arranged side by side in a first direction on a substrate, the first stack structure block including a first end portion that is flat and vertically extends above the substrate;
• a separation structure disposed on the substrate and disposed on a first sidewall of the first end portion of the first stack structure block;
• and
• first contact plugs penetrating the separation structure and arranged along the first sidewall of the first end portion.