A semiconductor device having a novel structure is provided. The semiconductor device includes a p-channel transistor and an n-channel transistor provided over a silicon substrate. One of a source and a drain of the p-channel transistor is electrically connected to a first power supply line, one of a source and a drain of the n-channel transistor is electrically connected to a second power supply line, and the other of the source and the drain of the p-channel transistor is connected to the other of the source and the drain of the n-channel transistor. The p-channel transistor includes a first gate electrode and a first back gate electrode provided to face the first gate electrode with a first channel formation region therebetween. The first back gate electrode is formed using a region where an impurity element imparting conductivity is selectively introduced to the silicon substrate. The n-channel transistor is provided above a layer including the p-channel transistor.