An SRAM device includes first, second and third transistors, which are used as a pass gate transistor, a pull-down transistor, and a pull-up transistor, respectively. A channel region of each transistor may include a plurality of semiconductor sheets that are vertically stacked on a substrate. The semiconductor sheets used as the channel regions of the first and second transistors may have a width greater than the semiconductor sheets used as channel regions of the third transistor.