PURPOSE: To increase breakdown voltage by disposing a high resistance film onto a second conductivity type low-concentration diffusion layer and a high resistance substrate on the out side of the diffusion layer through an insulating film in a high breakdown-voltage planar type semiconductor element in which the second conductivity type low-concentration diffusion layer is formed, surrounding a second conductivity type high-concentration diffusion layer in the first conductivity type high resistance substrate.

CONSTITUTION: A p+ type layer 2 in high impurity concentration is shaped to the surface of a high-resistance n- type Si layer 1, and a p- type layer 6 in low impurity concentration is formed around the layer 2. The total amount of an impurity per unit area at the time of viewing from the surface of the p- type layer 6 is specified to 1∼5.5×1012/cm2. An n+ type layer 9 is shaped around an element separated at a fixed distance from the p- type layer 6, and a semi-insulating polycrystalline silicon film 8 is disposed extending over the n+ type layer 9 from the p+ type layer 2 through an insulating film 7. When breakdown voltage of 70% of more is permitted at that time, the length of the p- type layer 6 extends over 120μm or less when the total amount of the impurity in the p- type layer exceeds 4×1012/cm2. When the p- layer is formed at two stages, however, the length of the layer in concentration exceeding 4×1012/cm2 may extend over 120μm or less.