Voltage withstanding structure for a semiconductor device

A semiconductor device comprising:

• a semiconductor substrate;
• a dielectric film formed on the semiconductor substrate;
• a first electrode and a second electrode separated from each other on the dielectric film;
• a spiral thin film layer having both ends connected to the first electrode and the second electrode, respectively, the spiral thin film layer surrounding the first electrode, the thin film layer being formed on the dielectric layer;
• and
• a plurality of p-n diodes formed in series in the spiral thin film layer along a longitudinal direction of the spiral thin film layer;
• wherein the semiconductor device is of a planar horizontal type;
• wherein the semiconductor substrate located between the first electrode and the second electrode constitutes an active region through which a main current flows, and
• the spiral thin film layer is formed on the semiconductor substrate through the dielectric film wherein a first region having a first conduction type in a surface layer of the semiconductor substrate, the first region connected to the first electrode;
• a second region having a second conduction type formed apart from the first region in the surface layer of the semiconductor substrate, the second region connected to the second electrode;
• and
• a third region having the second conduction type, the third region formed in the surface layer of the semiconductor substrate between the first region and the second region, the third region apart from the first region, the third region abutting on the second region, wherein the semiconductor substrate is of the first conduction type;
• wherein the semiconductor device satisfies the following conditions,
• VB<VZ×m
• where
• VB is the withstand voltage of the semiconductor device;
• VZ is the breakdown voltage of each of the p-n diodes;
• and
• m is the number of p-n junctions constituting the p-n diodes in the spiral thin film layer and placed in a reverse blocked state.