An interposer of a first semiconductor package includes a power supply wiring for a second semiconductor element, the power supply wiring including a land provided in one surface layer, and a power supply pattern provided in an inner layer and electrically connected to the land, the power supply wiring further including a larger number of lands than the land, which are provided in another surface layer and electrically connected in parallel to the power supply pattern. In a stacked semiconductor device, this configuration can improve the quality of power supply to the second semiconductor element to secure signal processing operation while preventing an increase in inductance caused by the bending of a power supply path in a power supply wiring of a printed wiring board or by a deviation of connection intervals.