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.