A semiconductor device with reduced power consumption can be provided. The semiconductor device includes a first transistor and a second transistor. The first transistor is a p-channel transistor including silicon in a channel formation region and the second transistor is an n-channel transistor including a metal oxide in a channel formation region. The metal oxide includes indium, an element M (e.g., gallium), and zinc. A gate of the first transistor is electrically connected to a gate of the second transistor, and one of a source and a drain of the first transistor is electrically connected to one of a source and a drain of the second transistor. The first transistor and the second transistor can each operate in a subthreshold region.