PURPOSE: To obtain an LDD type insulated-gate field-effect transistor of high breakdown strength and large current driving, with a small area.

CONSTITUTION: By forming a diffusion region 20 for preventing field inversion, only in an LDD which is formed in a field insulating layer 12 on the element isolation side, i.e., a second region 19 of a second conductivity type, the diffusion profile of a gate side LDD, i.e., a first region 18 of a second conductivity type can be adjusted, so that the output current and the breakdown strength of a transistor can be set to be the optimum values, to a semiconductor substrate 11 or a well region. The general depth of the diffusion region 20 for preventing field inversion is very large and a high breakdown strength is obtained to a semiconductor substrate or the like, so that the length in the element isolation direction can be reduced in the case of application to an LDD. Thereby an LDD type insulated-gate field-effect transistor of high breakdown strength, large current and small area can be realized.