Strong room-temperature photoluminescence (PL) was observed in the hydrogenated silicon-rich silicon nitride (a-SiNx:H) thin films grown by plasma-enhanced chemical vapor deposition technique. After the thermal annealing process, silicon nano-dots were clearly observed in the Si-rich a-SN0.56:H thin films. From the X-ray photoelectron spectroscopy (XPS), the Si 2p peak shows distinct Si-Si-4 bonds after thermal annealing indicated the existence of Si clusters. In addition, the existence of nano-crystallized (nc) Si dots was revealed from the image of high-resolution cross-section transmission electron microscopy (XTEM) analysis. The PL spectra exhibited extensive red-shift from 1.97 to 1.33 eV along with the annealing temperature suggests that, the Si nano-dot related luminescence dominates in the luminescence centers of the a-SiN0.56:H layer. The reveal of Si nano-dots related luminescence and the high density of Si nano-dots suggest that the a-SiN0.56:H layer is suitable for the stable light-emitting device. (C) 2003 Elsevier Science B.V. All rights reserved.