Barium titanate based semiconducting ceramics were synthesized using Ca 2+ and La 3+ as dopants, TiO 2 , SiO 2 and MnO as sintering aids, and various firing process. The Ca 2+ contained ceramics without impurity phases, sintered in reducing atmosphere and subsequent annealing in air, showed both the PTCR (Positive Temperature Coefficient of Resistivity) behavior and low room temperature resistivity µ RT 2.2 ³ cm. Based on knowledge of ionization energy and bond disassociation energy, it was cleared that Ca substitution plays an important role in lowering the µ RT value in the ceramics.