A semiconductor device capable of stably holding data for a long time is provided. A transistor including a back gate is used as a writing transistor of a memory element. In the case where the transistor is an n-channel transistor, a negative potential is supplied to a back gate in holding memory. The supply of the negative potential is stopped while the negative potential is held in the back gate. In the case where an increase in the potential of the back gate is detected, the negative potential is supplied to the back gate.