We studied infrared normal spectral emissivity on quasi-periodic microstructured silicon, which was prepared by femtosecond laser irradiation in SF6 ambient gas, coated with 100 nm thick Au thin film. The observed emissivity is higher than any reported previously for a flat material with a thickness of less than 0.5 mm, at a temperature range of 200 °C to 400 °C. The emissivity over the measured wavelength region increases with temperature and the spike height. These results show the potential to be used as a flat blackbody source or for applications in infrared thermal sensor, detector, and stealth military technology.