We report the observation of Wannier-Stark localization in a InGaAs-InAlAs superlattice waveguide. Using the oblique transition connecting electrons and holes localized in adjacent wells we achieve efficient intensity modulation at 1 . 57jim incident light wavelength under TE polarization mode. A 16 dB extinction ratio is obtained by applying a 0. 75V drive voltage to a 320 j. tm long waveguide. On-state attenuation is only 3 dB.