  It is demonstrated that the reason of SERS on dielectric and semiconductor
substrates is the enhancement of the electric field in the regions of the tops
of the surface roughness with very small radius, or a very large curvature. The
enhancement depends on the dielectric constant of the substrate and is stronger
for a larger dielectric constant. It is indicated that the enhancement on
dielectrics and semiconductors is weaker than on metals with the same modulus
of the dielectric constant. The result obtained is confirmed by experimental
data on the enhancement coefficients obtained for various semiconductor and
dielectric substrates.
