A method of manufacturing power-module substrates, after bonding copper-circuit plates 30 at intervals on a ceramic plate 21 having an area in which ceramic substrates can be formed abreast, by dividing the ceramic plate 21 between the copper-circuit plates 30, in which: bonding-material layers 71 of active-metal brazing material having same shapes as outer shapes of the copper-circuit plates 30 are formed on the ceramic plate 21; temporal-stick material 72 including polyethylene glycol as a major ingredient is spread on the copper-circuit plates 30, the bonding-material layers 71 and the copper-circuit plates 30 are temporarily fixed on the ceramic plate 21 in a state of laminating with positioning by the temporal-stick material 72; and a laminated assembly thereof is pressurized in a laminating direction and heated, so that the ceramic plate and the copper-circuit plates are bonded.