A semiconductor device includes a first semiconductor chip and a second semiconductor chip stacked on the first semiconductor chip. The second semiconductor chip includes a high-speed serial I/F circuit which transfers serial data between the high-speed serial I/F circuit and an external device through a serial bus, and transfers parallel data between the high-speed serial I/F circuit and an internal circuit included in the first semiconductor chip. A physical layer circuit of the high-speed serial I/F circuit is disposed on a first side of the second semiconductor chip which is the short side, and a logic circuit is disposed on a third side opposite to the first side.