A multilayer wiring structure for MMICs includes a power-supply wiring formed of a multilayer wiring (a plurality of power-supply lines). The wires are interconnected by throughholes. A power-supply current is divided and supplied to the lines. A large current can be supplied to the entirety of the multilayer wiring, even when the width of each of the lines is reduced. The multilayer wiring structure has an improved degree of freedom in the layout of wiring.