A semiconductor module radiator plate fabrication method includes soldering a plurality of insulating substrates of different shapes to a flat radiator plate, and forming a convex curve on an insulating substrate side of the radiator plate; obtaining a first concave curve by reversing the convex curve; setting a second concave curve on an insulating substrate side of a radiator plate after soldering, a bottom of the second concave curve being positioned under clearance between the plurality of insulating substrates; adding the first curve and the second curve to calculate a third concave curve on the insulating substrate side; and forming the third curve on a flat plate to form a radiator plate before soldering.