A memory device includes a mesa structure and a word line. The mesa structure, having two opposite side surfaces, includes at least one pair of source/drain regions and at least one channel base region corresponding to the pair of source/drain regions formed therein. The word line includes two linear sections and at least one interconnecting portion. Each linear section extends on the respective side surface of the mesa structure, adjacent to the channel base region. The at least one interconnecting portion penetrates through the mesa structure, connecting the two linear sections.