Semiconductor integrated circuit device and a method of producing the same

A semiconductor integrated circuit device has a read-only memory which comprises a plurality of first gate electrodes (5) arranged on a semiconductor substrate (1) in a first direction with a predetermined spacing therebetween, a plurality of second gate electrodes (7) that are arranged among the first gate electrodes (5) and partly overlap the first gate electrodes (5), and regions of data-writing impurities (9) positioned under the first and second gate electrodes (5,7). The impurities for writing data are introduced after the formation of the electrodes (5,7) through the first or second gate electrodes (5,7) using the over-lappings of the first and second gate electrodes (5,7) as masks. In this way, the time required for forming the device is reduced, and the area of the device occupied by the memory cells is reduced.