Photocurrent oscillations on n-type silicon (111) in acidic fluoride solutions lead to a reduction of the microscopic roughness on these surfaces, as investigated by Fourier transform infrared spectroscopy (FTIR) with attenuated total reflection techniques under in situ conditions, and by scanning tunneling microscopy (STM) performed in air. Roughness parameters obtained by STM measurements were reduced from 40 +/- 8 to 7 +/- 1 angstrom. The spatial and temporal synchronization during photocurrent oscillations leads to smoothing of large surfaces with a better result than applying an electropolishing treatment.