In the semiconductor device according to the present invention, a P type diffusion layer and an N type diffusion layer as a drain lead region are formed on an N type diffusion layer as a drain region. The P type diffusion layer is disposed between a source region and the drain region of the MOS transistor. When a positive ESD surge is applied to a drain electrode, causing an on-current of a parasite transistor to flow, this structure allows the on-current of the parasite transistor to take a path flowing through a deep portion of an epitaxial layer. Thus, the heat breakdown of the MOS transistor is prevented.