The total strain energy of a bilayer structure and the SSE always consist of two integral parts: the strain energy due to bending moment and due to axial force in the ratio 3:1.

The strain energy due to splitting forces has been isolated from the total strain energy of bilayer.

The strain energy due to splitting forces is proposed as the specific strain energy (SSE) for the bonding criterion.

The new SSE strongly depends on the thickness ratio of the layers and will even equal zero at a thickness ratio known as the point of equivalence. At the point of equivalence, even strong internal stresses do not affect the bonding strength of bilayer.

The point of equivalence has been calculated for five structures: Si/Al₂O₃, Si/GaAs, Si/LiNbO₃, Si/SiC, and Si/InP.