The semiconductor device includes the read circuit which reads data written to a memory cell. The read circuit includes a first transistor, a second transistor, a first switch, and a second switch. A first terminal of the first transistor is electrically connected to a gate of the first transistor, and a second terminal of the first transistor is electrically connected to an output from the read circuit via the first switch. A first terminal of the second transistor is electrically connected to a gate of the second transistor, and a second terminal of the second transistor is electrically connected to the output from the read circuit via the second switch. A channel formation region of the first transistor can be formed using an oxide semiconductor, and a channel formation region of the second transistor can be formed using silicon.