Although high Tc oxide superconductors have different chemical compositions, they are all perovskite‐type. In this paper, we define high Tc oxide superconductor‐forming elements, and show distribution of these elements in the periodic table. We present a novel expression from the high Tc perovskite‐type oxide superconductors, which is as simple as a chemical formula, but contains important structural information. Using this expression, we list most of known high Tc superconductors. We found that a perovskite‐type superconductor with certain layers of metallic atoms may reach a highest Tc, and the highest Tc is a function of total metallic atom layers: Tc(highest)=f×L (K) when L≤3×(E‐1), where E is the number of metallic elements, L is the number of metallic atom layers, and f is a coefficient. Therefore, higher Tc perovskite‐type superconductors should be sought in more complex systems.