A modification to the semiclassical treatmeat of rasonantly enhanced DFWM has been presented by considering the dependence of nonlinear polarization on cos(k·r). It hag been found that the phase-conjugate reflectivity obeys Ricoatti equation. Experiments are performed using a CW tunable CO2 laser and SF6 gas as nonlinear medium. The reflectivities of (0.2-0.8) ×10-4 are obtained.