A multi-chip semiconductor device includes a substrate, a first semiconductor chip, a second semiconductor chip, and a plastic mold. The first semiconductor chip has a function for executing a predetermined electrical operation and is installed on the substrate. The second semiconductor chip is installed on the first semiconductor chip and is configured to integrate a power circuit to receive an external power supply and to supply an electric power to the first semiconductor chip based on the external power supply. The plastic mold seals together the first and second semiconductor chips on the substrate.