In a semiconductor device, bonding-wires can be applied parallel to each other to electrodes of high-speed signal lines when mounting a highly densified semiconductor element on a low-cost substrate while reducing a length of the bonding-wires. An impedance-matched substrate having wiring that impedance-matched with circuits of a semiconductor element is mounted on a substrate. A plurality of first metal wires connect between first electrodes of the semiconductor element and electrodes of the substrate. A plurality of second metal wires connect between second electrodes of the semiconductor element and first electrodes of the impedance-matched substrate. A plurality of third metal wires connect between second electrodes of the impedance-matched substrate and electrodes of the substrate. The second metal wires extend parallel to each other, and the third metal wires also extend parallel to each other.