Patent ID: 7485922

Claim:
A semiconductor device comprising: a semiconductor substrate comprising a buried diffusion layer formed therein; a semiconductor layer disposed on the buried diffusion layer and comprising a first element formation region, a second element formation region and an isolation region isolating the first element formation region from the second element formation region, the isolation region comprising a first impurity diffusion layer of a first general conductivity type and a second impurity diffusion layer of the first general conductivity formed in the first impurity diffusion layer; a first semiconductor element formed in the first element formation region and comprising a third impurity diffusion layer of a second general conductivity type formed in the semiconductor layer; a second semiconductor element formed in the second element formation region and comprising a fourth impurity diffusion layer of the second general conductivity type formed in the semiconductor layer; a fifth impurity diffusion layer of the first general conductivity type disposed under the first impurity diffusion layer, wherein the third and fourth impurity diffusion layers form a PN junction with the first impurity diffusion layer and do not form a PN junction with the second impurity diffusion layer formed in the first impurity diffusion layer, the second impurity diffusion layer has an impurity concentration higher than the first impurity diffusion layer, the fifth impurity diffusion layer forms a PN junction with the buried diffusion layer, and the fifth impurity diffusion layer has an impurity concentration lower than the first impurity diffusion layer.