A power semiconductor device module includes: a base plate; an insulating substrate mounted on the base plate; and a diode chip mounted on the insulating substrate, wherein the insulating substrate has an upper surface electrode layer disposed on an upper main surface and a lower surface electrode layer disposed on a lower main surface, the diode chip is joined onto the upper surface electrode layer, the lower surface electrode layer is joined onto the upper main surface of the base plate, and a thermal resistance reducing section that reduces thermal resistance is provided in lower surface electrode layer or the base plate of a portion corresponding to a place immediately below the diode chip.