A semiconductor device includes a first layer, a second layer over the first layer, and a third layer over the second layer. The first layer includes a first transistor. The third layer includes a second transistor. A channel formation region of the first transistor includes a single crystal semiconductor. A channel formation region of the second transistor includes an oxide semiconductor. The second layer includes a first insulating film, a second insulating film, and a conductive film. The conductive film has a function of electrically connecting the first transistor and the second transistor. The first insulating film is over and in contact with the conductive film. The second insulating film is provided over the first insulating film. The second insulating film includes a region with a carbon concentration of greater than or equal to 1.77×1017 atoms/cm3 and less than or equal to 1.0×1018 atoms/cm3.