We report the results of measurements of the electrically induced refractive index change caused by the free‐carrier effect in a silicon Schottky diode. We find that for the wavelength &lgr;=1.3 &mgr;m, the real part of the refractive index changes by as much as ‖&Dgr;n‖∼0.01 for current densities less than 1 A/cm2. This refractive index change produced changes in the input‐coupling efficiency as large as 75% in our sample geometry.