To provide a semiconductor device including a volatile memory which achieves high speed operation and lower power consumption. For example, the semiconductor device includes an SRAM provided with first and second data holding portions and a non-volatile memory provided with third and fourth second data holding portions. The first data holding portion is electrically connected to the fourth data holding portion through a transistor. The second data holding portion is electrically connected to the third data holding portion through a transistor. While the SRAM holds data, the transistor is on so that both the SRAM and the non-volatile memory hold the data. Then, the transistor is turned off before supply of power is stopped, so that the data becomes non-volatile.