PURPOSE: To prevent relaxing effect of electric field from lowering at the edge of a drain by permitting the insulating film sandwiched by a source electrode interconnecting film and the drain area to be thinner than an insulating film sandwiched by the drain electrode interconnecting film and the drain area.

CONSTITUTION: A drain electrode interconnecting film 15 is constituted of a part 15a which makes ohmic contact with an N+ drain area 23a and an extending part 15b which faces the drain areas 23a and 3b through an interlayer insulating film 17 and the laminating insulating film of a gate oxide film 6. A part which extends from a source electrode interconnecting film 34 and overlaps with an N- drain area 3b is permitted to be a field plate 34a. The width of the field plate 34a is reduced and the insulating film under the field plate 34a is formed thinner than the insulating film under the drain electrode interconnecting film 15b. Thus, the electric field at the drain edge is relaxed.