A memory device includes transistor structures and memory arc wall structures. The memory arc wall structures are embedded in the transistor structures. The transistor structure includes a dielectric column, a source electrode and a drain electrode, a gate electrode layer and a channel wall structure. The source electrode and the drain electrode are located on opposite sides of the dielectric column. The gate electrode layer is around the dielectric column, the source electrode, and the drain electrode. The channel wall structure is extended from the source electrode to the drain electrode and surrounds the dielectric column. The channel wall structure is disposed between the gate electrode layer and the source electrode, between the gate electrode layer, and the drain electrode, and between the gate electrode layer and the dielectric column. The memory arc wall structure is extended on and throughout the channel wall structure.