Semiconductor device substrate and method for producing semiconductor device substrate

A method for producing a semiconductor device substrate, the method comprising:

• a first step of preparing a ceramic substrate including a first surface and a second surface;
• a second step of forming a brazing material layer on the first surface and the second surface;
• a third step of disposing a copper plate on the brazing material layer to obtain an intermediate product including the ceramic substrate, the brazing material layer, and the copper plate;
• and
• a fourth step of disposing the intermediate product in a furnace and performing a heating and pressurizing treatment,
• wherein, in the fourth step, after a temperature of the intermediate product is increased to 800 to 900° C., the intermediate product is cooled to a softening point of copper constituting the copper plate at a first average cooling rate of 2.8 to 12° C./min.