For a multi-terminal semiconductor package, such as a BGA or a CSP, that handles high-speed differential signals, a high-speed signal is assigned to the innermost located electrode pad on an interposer substrate, and the electrode pad is connected to the outermost located ball pad on the interposer substrate. With this arrangement, the length of a plating stub can be considerably reduced, and the adverse affect on a signal waveform can be minimized. This arrangement is especially effective for differential signal lines.