SEMICONDUCTOR DEVICE

PURPOSE:To enable breakdown voltage to be set irrespective of an oxide film on the surface or a surface level by constructing a Zener diode from an N-type diffusion layer, formed in a region of an epitaxial layer surrounded by an isolation layer, and a P-type buried layer, connected to a semiconductor substrate, and achieving breakdown of the Zener within a semiconductor device. CONSTITUTION:Deposition for a P-type high concentration buried layer 12 is carried out on the upper surface of a P-type silicon substrate 11, and an N-type epitaxial layer 13 is formed thereon, and deposition for an isolation layer 14 and deposition for N-type high concentration diffusion layer 15 are carried out on the upper surface of the epitaxial layer 13, and heat treatment is effected to form the buried layer 12, the isolation layer 14, and the diffusion layer 15. A voltage is applied between the diffusion layer 15 and the isolation layer 14 to make the diffusion layer 15 side positive, and when that voltage exceeds the breakdown voltage formed between the diffusion layer 15 and the buried layer 12, breakdown takes place at the contact surface between the diffusion layer 14 and the buried layer 12, a current flows through an electrode 16, the diffusion layer 15, the buried layer 12, and the isolation layer 14. At that time, the breakdown does not take place at the surface, so that the breakdown voltage is not affected by the state of that surface.