A metal oxide semiconductor (MOS) transistor has a source terminal, a drain terminal, a gate terminal and a body terminal. The source terminal is connected to receive a supply voltage and the body terminal is connected to receive a reverse body bias voltage. A photovoltaic circuit has a first terminal connected to the source terminal of the MOS transistor and a second terminal connected to the body terminal of the MOS transistor. The photovoltaic circuit converts received photons from the environment to generate the reverse body bias voltage.