A semiconductor device comprises a first transistor and a potential generator circuit. The first transistor has a first conduction type first semiconductor region and a second conduction type second semiconductor region formed in the first semiconductor region. The first and second semiconductor regions are supplied with first and second prescribed potentials, respectively. The potential generator circuit generates the first prescribed potential. The potential generator circuit has a first power supply terminal supplied with a first power supply potential, a second power supply terminal supplied with a second power supply potential set to a higher potential than the first power supply potential, and an output terminal outputting the first prescribed potential. The potential generator circuit outputs the second power supply potential when the second power supply potential is higher than a predetermined potential, and the first power supply potential when the second power supply potential is lower than the predetermined potential.