PURPOSE: To enable data to be written-in and read out of a memory device rapidly, by injecting electrons from a first interconnection into an island region by means of the tunnel effect when data is to be written-in and injecting electrons from the island region into the first interconnection by means of the tunnel effect when data is to be read out.

CONSTITUTION: In an insulation film 3, an island-type floating electrode 4 is arranged at each of intersections defined by a plurality of Y address electrodes 1 and a plurality of X address electrodes 2. The region 3a of the insulating film 3 located between the floating electrode 4 and the Y address electrode 1 is formed to have a thickness (d1) small enough to cause tunnel effect, for example a thickness of about 10∼30. On the contrary, the region 3b between the floating electrode 4 and the X address electrode 2 has a thickness (d2) about twice as large as (d1), for example a thickness of about 50ρ so that tunnel effect is prevented. A memory cell 5 serving as a storage unit is provided for each of these floating electrode 4. In this manner, data can be rapidly written-in or read out of a memory device having construction suitable for high density packaging and high integration.