A method for producing a substrate for a power module with a heat sink that comprises a ceramic substrate, a first metal plate made of aluminum with one surface being bonded to a surface of said ceramic substrate, a second metal plate (13, 23) made of aluminum with one surface being bonded to a rear surface of said ceramic substrate, and a heat sink made of aluminum or aluminum alloy and bonded to the other surface of said second metal plate (13, 23), which is opposite to said one surface bonded to said ceramic substrate, said method comprising: a ceramic substrate bonding step for bonding said ceramic substrate and said first metal plate, and for bonding said ceramic substrate and said second metal plate (13, 23); and a heat sink bonding step for bonding said heat sink to the other surface of said second metal plate (13, 23), and said heat sink bonding step comprises; a Cu layer forming step for forming a Cu layer by fixing Cu to at least one of the other surface of said second metal plate (13, 23) and a bonding surface of said heat sink; a heat sink laminating step for laminating said second metal plate (13, 23) and said heat sink via said Cu layer; a heat sink heating step for pressing in the lamination direction and heating said laminated second metal plate (13, 23) and said heat sink, to form a molten metal area in an interface between said second metal plate (13, 23) and said heat sink; and a molten metal solidifying step for solidifying the molten metal area thereby bonding said second metal plate (13, 23) and said heat sink, wherein in said heat sink heating step, Cu in said Cu layer is diffused into said second metal plate (13, 23) and said heat sink, thereby forming said molten metal area in the interface between said second metal plate (13, 23) and said heat sink, and wherein in the molten metal solidifying step, the temperature is maintained constant in a state with the molten metal area being formed, then the Cu in the molten metal area diffuses toward the second metal plate (13, 23) and the heat sink, consequently, a Cu concentration in the portion being the molten metal area gradually decreases to increase the melting point, and solidification proceeds in a state with the temperature being maintained constant. a ceramic substrate bonding step for bonding said ceramic substrate and said first metal plate, and for bonding said ceramic substrate and said second metal plate (13, 23); and a heat sink bonding step for bonding said heat sink to the other surface of said second metal plate (13, 23), and said heat sink bonding step comprises; a Cu layer forming step for forming a Cu layer by fixing Cu to at least one of the other surface of said second metal plate (13, 23) and a bonding surface of said heat sink; a heat sink laminating step for laminating said second metal plate (13, 23) and said heat sink via said Cu layer; a heat sink heating step for pressing in the lamination direction and heating said laminated second metal plate (13, 23) and said heat sink, to form a molten metal area in an interface between said second metal plate (13, 23) and said heat sink; and a molten metal solidifying step for solidifying the molten metal area thereby bonding said second metal plate (13, 23) and said heat sink, wherein in said heat sink heating step, Cu in said Cu layer is diffused into said second metal plate (13, 23) and said heat sink, thereby forming said molten metal area in the interface between said second metal plate (13, 23) and said heat sink, and wherein in the molten metal solidifying step, the temperature is maintained constant in a state with the molten metal area being formed, then the Cu in the molten metal area diffuses toward the second metal plate (13, 23) and the heat sink, consequently, a Cu concentration in the portion being the molten metal area gradually decreases to increase the melting point, and solidification proceeds in a state with the temperature being maintained constant.