Reduction of reflection is of great importance in optical spectroscopy to reduce interference and increase throughput. Here we demonstrate a three-dimensional inverted photonic grating device design using only one material—silicon. Enhanced transmission compared to planar silicon wafers is observed from $0.2\mathrm{THz}$ to over $7.3\mathrm{THz}$ for a device with a $15\mathrm{\mu m}$ period, which covers most of the terahertz band, and its relative $3\mathrm{dB}$ bandwidth $(\delta f/f_c)$ is a noteworthy 116.3%. Moreover, the device is polarization independent and can perform up to a large incident angle.