Objective of the article is to support the understanding and identification of the mechanism involved in the SERS phenomenon. It is usually believed that two types of enhancement mechanisms involved for the huge enhancement of SERS spectra over Raman spectra. One is a long-range electromagnetic (EM) effect and the other is a short-range chemical (CHEM) effect, are simultaneously operative. The EM mechanism is established on the amplified electromagnetic field produced by optical excitation of surface plasmon resonance of nano-scale surface roughness. On the other hand, the photo induced transfer of the electrons (transfer of charge) from the Fermi level of the metal to the unoccupied molecular orbital of the molecule or molecule to metal is depended completely on the energy of the photon and the electric potential of the interface.