A method is provided for easily producing thick multi-layer substrates maintaining highly accurate resistances with little variation. A thick-film resistor 6 on a ceramic substrate 1 is fired at a temperature higher than the temperature of firing a glass insulating layer 2 that is formed thereon in contact therewith. This makes it possible to decrease the change in the resistance in a subsequent high-temperature step of firing the glass insulating layers 2 to 4. Moreover, after the glass insulating layer 2 is formed on the thick-film resistor 6 on the ceramic substrate 1, laser trimming is effected through a window or the glass insulating layer 2 and, thereafter, the glass insulating layers 3 and 4 are formed. This makes it possible to decrease the change in the resistance of the thick-film resistor 6 after laser trimming and to reduce the laser output.