A memory device and method of forming the same are provided. The memory device includes a first memory cell disposed over a substrate. The first memory cell includes a transistor and a data storage structure coupled to the transistor. The transistor includes a gate pillar structure, a channel layer laterally wrapping around the gate pillar structure, a source electrode surrounding the channel layer, and a drain electrode surrounding the channel layer. The drain electrode is separated from the source electrode a dielectric layer therebetween. The data storage structure includes a data storage layer surrounding the channel layer and sandwiched between a first electrode and a second electrode. The drain electrode of the transistor and the first electrode of the data storage structure share a common conductive layer.