Making the chemical or biological sensors simpler and more compatible with other measurements is a key enabling technology for commercial application. In this work, we propose a plasmonic refractive-index sensor only based on gold/silicon Schottky junction to simultaneously perform optical and electrical read-out responses. Via exciting surface plasmon resonance (SPR), the designed device shows a few characteristic reflection valleys and greatly enhances the narrowband light absorption. Calculated results indicate that the SPR resonance wavelength can be tuned in the wavelength range of 1100-2000 nm by manipulating the period, width of the Si nanochannel and the incident angle of light. When the analyte is changed, the SPR resonance wavelength generated at the bottom surface of the Au layer barely shifts, while the one at the top surface shows a significant linear shift. The optimally designed system shows an optical response with a refractive index sensitivity of over 1000 nm per refractive index unit (nm/RIU). Moreover, the electrodynamic calculation of the hot electrons predicts the electrical response can be up to 14.5 mA/(W·RIU) for an example of detecting trichloromethane, where the employed light can be a monochromatic light and the sensing operation can be much simpler relative to the conventional spectral work mode.