By analyzing various experimental photoluminescence (PL) and photoluminescence excitation (PLE) spectra in porous silicon (PS), we have found that the PL spectra in PS are characterized by the transitions among the quantum confined states in nanoscale Si which are influenced by the surface chemical bonds. Since the size of silicon filament is comparable to that of surface potential, its electron states are modified by the surface potential. We use a two-dimensional state-dependent surface potential to model the overlapping of surface chemical bonds, from which we obtain a new set of quantum confined states modified by the surface potential. By using these new quantum states the effective luminescence, experimental PL, and PLE spectra in porous Si are well explained. ©1997 American Institute of Physics.