In a method of manufacturing an SRAM, first dummy patterns are formed over a substrate, on which a first to a third mask layer are formed. Intermediate dummy patterns are formed on sidewalls of the first dummy patterns. The first dummy patterns are removed, thereby leaving the intermediate dummy patterns. The third mask layer is patterned by using the intermediate dummy patterns, by which the second mask layer is patterned, thereby forming second dummy patterns. Sidewall spacer layers are formed on sidewalls of the second dummy patterns. The second dummy patterns are removed, thereby leaving the sidewall spacer layers as hard mask patterns over the substrate, by which the first mask layer is patterned. The substrate is patterned by using the patterned first mask layer. Each of the plurality of SRAM cells is defined by a cell boundary, within which only two first dummy patterns are included.