The energy location for the interface state densityNssminimum of the insulator–semiconductor (I–S) interface and the Fermi‐level pinning position at the metal–semiconductor (M–S) interface are shown to coincide and to lie at the same position of 5.0 eV from the vacuum level for major tetrahedral semiconductors. Neither the unified defect model nor the metal induced gap state model can explain the novel striking correlation between the I–S and M–S interfaces. The correlation as well as the observed peculiar photoionization behavior of the I–S interface are explained by the novel unified disorder induced gap state (DIGS) model where DIGS pin or restrict the movement of the surface Fermi level. The above characteristic energy,EHO, is shown to be the Fermi energy of the DIGS spectrum which is given by the hybrid orbital energy of thesp3bond of the host. The DIGS model explains remarkably well the behavior of the M–S interface formed on the bare or oxide covered semiconductor surface as well as the various features ofNssdistribution of the I–S interface. The correlation between the DIGS‐free heterojunction (S–S) interface and M–S/I–S interface is explained by the fact thatEHOis a universal reference energy level of the host which is invariant under any off‐diagonal interactions, as is evidenced by the alignment of transition metal deep levels, DX centers and EL2 with respect toEHO. Band offset at the S–S interface is proposed to be determined by the alignment ofEHOwhich inevitably involves formation of interface dipole when twoEHOlevels lie at different positions from the vacuum level.