US Patent 9685500 Circuit system

A semiconductor device with a transistor having favorable electrical characteristics is provided. The semiconductor device has a memory circuit and a circuit that are over the same substrate. The memory circuit includes a capacitor, a first transistor, and a second transistor. A gate of the first transistor is electrically connected to the capacitor and one of a source and a drain of the second transistor. The circuit includes a third transistor and a fourth transistor that are electrically connected to each other in series. The first transistor and the third transistor each include an active layer including silicon, and the second transistor and the fourth transistor each include an active layer including an oxide semiconductor.