US Patent 7420281 Stacked chip semiconductor device

A stacked chip semiconductor device whose size is substantially reduced by high density packaging of two or more semiconductor chips. In the semiconductor device, four semiconductor chips are stacked over a printed wiring board. The bottom semiconductor chip has an interface circuit which includes a buffer and an electrostatic discharge protection circuit. All signals that these semiconductor chips receive and send are inputted or outputted through the interface circuit of the bottom semiconductor chip. Since the other semiconductor chips require no interface circuit, the semiconductor device is compact.