We present the simulation, fabrication, and characterization of a metallic slot grating on a silicon waveguide (30nm slot width for a period of 500nm). According to the simulation, the experimental measured spectrum of the structure exhibits a dip in the near-infrared region. Moreover, the finite-difference time-domain simulation shows that this device can be used as a sensor, due to its high sensitivity to the refractive index variation of the medium above and inside the cavity (η ¼ Δλ=Δn ¼ 750nm=refractive index unit).