Plasmon-induced hot electrons have attracted a great deal of interest as a novel route for photodetection and light energy harvesting. In this work, we investigate the plasmonic properties of AuSi as a novel plasmonic material for hot-electron infrared photodetection. Calculation by the Bruggeman’s theory shows that the plasma frequency is red-shifted with decreasing gold filling ratio. A plasmonic nanostructure with a periodic grating is then designed for surface plasmon excitation. The absorbance by AuSi can reach 0.87 at a wavelength of 2000nm due to the surface plasmon resonance on metal stripes. The AuSi nano-antenna array is adopted to improve the absorbance up to 95% with polarization independence. AuSi possesses much lower free electron concentration than Au, and thus longer mean free path of hot electrons. With adjustable Schottky barrier, the proposed AuSi-Si hot electron detector may have potential in fields of silicon-based integrated photonics and infrared imaging.