A power-module substrate includes first and second sets of circuit-layer metal-plates, a first ceramic substrate, a metal member connecting the first and second sets of circuit-layer metal-plates through a hole formed in the first ceramic substrate, a second ceramic substrate, a heat-radiation-layer metal-plate, and an electric component attached to a top surface of one of the first set of circuit-layer metal-plates above the metal member and the through hole. The power-module substrate is configured to conduct heat from the electric component through the through hole via the metal member, along the second set of circuit-layer metal-plates, and to the heat-radiation-layer metal-plate.