Abstract: An undercoat containing copper and bismuth and/or vanadium is formed on a ceramic substrate such as Al.sub.2 O.sub.3. When the undercoat contains copper and bismuth, the ceramic substrate having the undercoat is heated at a temperature between 600.degree. C. and 1100.degree. C. in an oxidative atmosphere to obtain a fired undercoat on the ceramic substrate. The fired undercoat is formed with copper oxide particles and a binder phase containing bismuth and copper for bonding between adjacent copper oxide particles. A bismuth content in the fired undercoat is determined within a range of 10 to 90 wt %. When the undercoat contains copper and vanadium, the ceramic substrate having the undercoat is heated at a temperature between 450.degree. C. and 1100.degree. C. in the oxidative atmosphere to obtain a fired undercoat which is formed with copper oxide particles and a binder phase containing vanadium and copper. A vanadium content in the fired undercoat is determined within a range of 3 to 63 wt %.