Porous silicon has been subjected to NF3/UV photochemical surface treatment in the range of 300-4000C. This treatment is found to enhance strongly the photoluminescence of porous silicon by couple orders of magnitude. The effect of photoluminescence enhancement has been observed only when the NF3 treated porous silicon was exposed to air environment. The photoluminescence intensity continued to grow with the aging time in air, even at the room temperature. Using atomic force microscope, scanning electron microscope and Auger measurements, it is found that the photoluminescence enhancement correlated with the formation of crystalline oxide layer at the porous silicon surface. This oxide layer SiOx (x≅2) is much more stoichiometric as compared to the native oxide SiOx (x≅1) covering the reference porous silicon surface (not treated by NF3). The rapid growth of the SiO2 layer is supposed to be due to the NF3/UV photo-thermal etching of the as-formed native oxide as well as to the cleaning and passivation of the porous silicon surface with fluorine.