PURPOSE: To facilitate writing into a junction breakdown writing type memory device and to obtain a high speed and high density, by constituting said memory device on an insulating layer in a plane shape.

CONSTITUTION: On an insulating layer 2 formed on a substrate 1, a first conductive type first region 4, a second conductive type second region 5, and a first conductive type third region 6 are formed in a plane shape. An electrode 8 of a conductor is provided at least at a part over the first region 4. A junction 10 between the first region 4 and the second region 5 is broken and information is written. In this constitution, since a writing current is small and a parasitic capacity is also small, a high speed is obtained. Furthermore, a decoupling diode and the like for preventing the runaround current are not required, and the device can be made compact.