Grain boundary layer dielectric ceramic compositions comprising semiconductive ceramic grains having a composition of 50.23 to 49.47 mol % of SrO and CaO, 49.72 to 50.23 mol % of TiO.sub.2, 0.05 to 0.3 mol % of Nb.sub.2 O.sub.5, substantially each of said grains being surrounded by grain boundary layer dielectric materials which are formed by grain boundary diffusion of a mixture having a composition of 93.5 to 8.5 mol % of Bi.sub.2 O.sub.3, 4.5 to 45 mol % of Cu.sub.2 O, 0.5 to 4 mol % of MnO.sub.2, 1 to 8.5 mol % of B.sub.2 O.sub.3, 0.5 to 17 mol % of La.sub.2 O.sub.3, and below 17 mol % of TiO.sub.2.These ceramic compositions provide capacitors having a temperature coefficient of capacitance less than .+-.15%, an apparent dielectric constant higher than 35,000, a dielectric loss less than 0.01 and a breakdown voltage higher than 500 V/mm; or capacitors having a temperature coefficient of capacitance less than .+-.10%, an apparent dielectric constant higher than 20,000, a dielectric loss less than 0.01 and a breakdown voltage higher than 700 V/mm; or capacitors having a temperature coefficient of capacitance less than .+-.5%, an apparent dielectric constant higher than 5,000, a dielectric loss less than 0.01 and a breakdown voltage higher than 700 V/mm.