Patent ID: 7664895

Claim:
A semiconductor device comprising: a first semiconductor chip; and a second semiconductor chip stackable above the first semiconductor chip, the second semiconductor chip including an interface circuit that transfers serial data between the interface circuit and an external device through a serial bus, and transfers parallel data between the interface circuit and an internal circuit included in the first semiconductor chip, the interface circuit including an internal interface circuit that transfers parallel data between the interface circuit and the internal circuit included in the first semiconductor chip, the second semiconductor chip being set to a first interface mode when the second semiconductor chip is used as a single chip instead of stacking the second semiconductor chip above the first semiconductor chip, the second semiconductor chip being set to a second interface mode when the second semiconductor chip is stacked above the first semiconductor chip, the internal interface circuit included in the second semiconductor chip transferring K-bit parallel data in the first interface mode, the internal interface circuit included in the second semiconductor chip transferring J-bit (J<K) parallel data between the interface circuit and the internal circuit included in the first semiconductor chip in the second interface mode, and a bit number of J-bit parallel data transferred in the second interface mode being smaller than a bit number of K-bit parallel data transferred in the first interface mode.