A mask read-only memory (ROM) includes parallel doping lines of a second conductivity type formed in a substrate of a first conductivity type, a first insulation film formed on the doping lines and the substrate, conductive pads fainted on the first insulation film, a second insulation film formed on the first insulation film and the conductive pads, parallel wires formed on the second insulation film extending perpendicular to the doping lines, contact plugs formed in the first insulation film that connect the doping lines to the conductive pads, and vias formed in the second insulation film that connect the conductive pads to the wires, wherein crossings of the doping lines and the wires define memory cells, contact plugs and vias are formed in memory cells of a first type, and at least one of the contact plug and via are missing from memory cells of a second type.