The visible light emission from KrF excimer laser crystallized a-Si:H/a-SiN x:H multi-quantum well (MQW) films at room temperature is reported. Both X-ray diffraction (XRD) and Raman scattering spectra provide evidence for the crystallization of Si layers within the MQWs after laser annealing treatment. Transmission electron micrographs (TEM) show the perfect conservation of the layered structures and proves the mechanism of constrained crystallization by stable a-SiN x :H barrier layers during laser annealing. The peak wavelength of visible PL spectra of the crystallized samples is around 640 nm (∼ 1.94 eV) and does not shift with different exposure energy. The FWHM of the PL peak becomes narrower to 0.4 eV when the irradiation energy density is increased to 0.9 J/cm 2.