The optoelectronic properties of porous Si (PS) have been investigated in relation to the visible luminescence characteristics. First, the electronic structure has been characterized by spectroscopic ellipsometry and synchrotron orbital radiation (SOR) reflection spectra analyses. A retention of the original crystallinity, accompanied by a band gap widening, is confirmed by the optical reflection spectra and the optical constants behavior. Second, it is shown that there exists an intrinsic correlation between the visible photoluminescence characteristics of PS and its interfacial and electrical properties. These experimental results suggest that in the visible luminescence mechanism of PS, both band modification in Si crystallites and passivation at their surface play a complementary role to each other. The former ensures sufficient electronic excitation and the latter contribute to suppression of nonradiative relaxation.