In order to explain the mechanism leading to unusual strong pairing of electrons (holes) within the conducting Cu-0 layers in YBa2Cu307-like high temperature superconductors, a novel model involving the exchange coupling of electrons at the X2-y2 and Z2 Cu levels is suggested. It is shown that the virtual bound states originating from conduction electrons and z2-level electrons play a role of two-particle states. The coupling between such bound states with the total energy close to E(F) and conduction electrons results in high values of T(c) and arbitrary ratios 2-DELTA/T(c) dependent on the energy parameters of the problem. In the framework of the given theory a number of experimental data on HTSC may be explained readily.
