This invention offers a ROM in which a user can program his digital data. In a memory cell array of the ROM, in which a plurality of interlayer insulation layers and a plurality of metal layers (including a bit line which makes an uppermost layer) are alternately stacked over each memory transistor, an insulation layer is formed on a tungsten plug in a first contact hole provided in a first interlayer insulation layer. The ROM is programmed by writing digital data "1" or "0" in each of the memory transistors according to whether a dielectric breakdown of the insulation layer is caused by a predetermined programming voltage (high voltage) applied from the bit line.
