Photoluminescence (PL) properties of SiNx (0.51 < x < 1.3) films are studied. A visible luminescence near the UV region is observed and the PL intensity and peak positions are found to be governed by the excess silicon composition. A large scale potential fluctuation due to the spatial variation of chemical composition in SINx is proposed to explain these observations, In addition, non-radiative recombination centers (N3Si ., N2SiSi ., NSi2Si ., or Si3Si .), which have prominent effect on the luminescence intensity, are also studied using electron spin resonance (ESR) measurement. The ESR results suggest that the excess silicon content should not be too high in order to have a strong PL.