A single-sided access device includes an active fin structure comprising a source contact area and a drain contact area separated from each other by an isolation region therebetween; a trench isolation structure disposed at one side of the active fin structure, wherein the trench isolation structure intersects with the isolation region between the source contact area and the drain contact area; a sidewall gate disposed under the isolation region and on the other side of the active fin structure opposite to the trench isolation structure so that the active fin structure is sandwiched by the trench isolation structure and the sidewall gate, wherein the sidewall gate has multi-fingers that engage with the active fin structure; and a gate dielectric layer between the sidewall gate and the active fin structure.