A solid-state relay having favorable electrical characteristics is provided. The solid-state relay includes a first circuit and a second circuit. The first circuit includes a first light-emitting element. The second circuit includes a first light-receiving element, a memory, and a first switch. The memory includes a second switch. The second switch includes a second semiconductor layer. The first switch and the first light-emitting element are formed using a first semiconductor layer. The first semiconductor layer and the second semiconductor layer contain gallium, and the second semiconductor layer further contains oxygen. On or off of the first light-emitting element is controlled by a first signal supplied to the first circuit. First data, which is generated when the first light-receiving element converts light emitted by the first light-emitting element into voltage, is supplied to the memory. Conduction or non-conduction of the first switch is controlled by the first data stored in the memory.