a semiconductor device in a continuous diffusion region formed on a semiconductor substrate and having either a p - type or n - type polarity includes : a first transistor formed within the continuous diffusion region ; a second transistor formed within the continuous diffusion region and in an area that is different from an area where the first transistor is formed ; a third transistor formed within the continuous diffusion region and in an area between the first and second transistors , and having a gate electrode to which a fixed potential is applied ; and a fourth transistor formed within the continuous diffusion region and in an area between the second and third transistors , and having a gate electrode to which a fixed potential is applied .