The effect of electric field on the photoluminescence and absorption spectra of porous silicon were investigated. An electric field applied perpendicular to the porous silicon growth direction shows a red shift in the photoluminescence peak energy and quenching of the photoluminescence intensity, whereas an electric field applied parallel to the growth direction shows photoluminescence quenching, but no clear indication of red shift. The absorption spectra also show a red shift of the absorption edge together with an increase in the absorption coefficient when an electric is field applied perpendicular to the porous silicon growth direction. The results are qualitatively similar to the quantum confined Stark effect, and provide additional support for quantum size effect as the mechanism of light emission in porous silicon.