A semiconductor device includes a first transistor formed on a substrate and including first and second impurity regions, a second transistor formed on the substrate and including a third impurity region electrically connected to the second impurity region, and a fourth impurity region, a power supply terminal electrically connected to the first impurity region, a ground terminal electrically connected to the fourth impurity region, a first guard ring surrounding the first transistor in a plan view and electrically connected to the ground terminal, and a second guard ring surrounding the second transistor in a plan view and electrically connected to the ground terminal. A conductivity type of the first through fourth impurity regions is different from a conductivity type of the first and second guard rings. The second guard ring has a width narrower than a width of the first guard ring in a plan view.