It is tried to empirically understand the superconducting critical temperature T c of various materials (24 elements, 286 A n B (n=1, 2, 3) compounds, 34 Fe- and 49 Cu-based compounds) by the effective pseudopotential radius, r(eff), and the effective orbital electronegativity, χ(eff)(=[N(v)/r(eff)] 1/2 ). By giving the sets of values of r(eff) and the number of effective electron, N(v), for 65 elements under the assumption that both the hybridization state and N(v) can be assigned to 65 elements in advance by considering their electronic characters, the T c /N(atom)–χ(eff) and T c –N(v)r(eff) 3 relations are examined, where N(atom) is the number of atom in compounds. It is found that a convex triangle-like relation is obtained between T c /N(atom) and χ(eff) and the maximum of T c /N(atom) is observed at around the threshold χ(eff) corresponding to metal–semiconductor transition. The cuprates and Fe-compounds with the χ(eff) closer to the threshold value show the higher T c value. Applying the linear relation between T c and N(v)r(eff) 3 empirically obtained for the elements to the compounds, it is indicated that about two-thirds of A n B compounds as well as the Fe- and Cu-based compounds are well placed along the linear relation. These results allow us to estimate the T c value in compound materials empirically based on the effective pseudopotential radius determined by the assumed hybridization.