This silicon avalanche mode light emitting device(Si AM LED) was fabricated with N+PN+PN+ cascade structure by using polycrystalline silicon material. When the LED operates in an appropriate voltage, the visible light with wavelength ranging from about 400 nm to 900 nm can be observed at the reverse-biased junctions. Thanks to the cascade structure, the optical emission intensity can be enhanced through the minority carrier injection from the forward-biased junctions. Based on this Si AM LED, coupled with silicon nitride optical waveguides and silicon P-I-N detectors(for example), monolithic integration of all-silicon biosensing device could be realizable.