A memory device including a substrate, a stack structure, an isolation structure, an inter-gate dielectric layer, a control gate, a first insulation structure, a first gate dielectric layer, and a first gate. The stack structure is disposed on the substrate. The isolation structure is disposed in the substrate and disposed at two sides of the stack structure. The inter-gate dielectric layer covers the stack structure and the isolation structure. The control gate covers the inter-gate dielectric layer. The first insulation structure is disposed in the substrate, wherein a top surface of the first insulation structure is lower than a top surface of the substrate, so that a side surface of a portion of the substrate is exposed. The first gate dielectric layer is disposed on the top surface and the side surface of the substrate. The first gate covers the first gate dielectric layer.