A memory device memory device includes a multi-layers stack, a charge-trapping layer, a first channel layer and a SSL switch. The multi-layers stack includes a plurality of insulating layers, a plurality of conductive layers alternatively stacked with the insulating layers and at least one first through opening passing through the conductive layers. The charge-trapping layer blankets over a sidewall of the first through opening. The first channel layer is disposed in the first through opening. The SSL switch is disposed on the multi-layers stack and includes a second channel layer, a gate dielectric layer and a gate. The second channel layer is disposed on and electrically contacting to the first channel layer. The gate dielectric layer is disposed on the second channel layer and made of a material other than that for making the charge-trapping layer. The gate is disposed on the gate dielectric layer.