We report on the voltage quenching of photoluminescence (PL) from p-type porous Si (PS) with a nanoporous structure. The voltage quenching effect has been studied using samples with different types of solid stale contacts and the effect on quenching examined. X-ray photoelectron spectroscopy (XPS) has been used to examine chemical evolution on the surface of free standing PS during the application of an external bias. In addition to this, XPS has also been used to study the valence band of porous silicon during the application of an electric field, in order to study the depletion of carriers from the nanocrystallites. II is believed that this is an important factor in the voltage-quenching effect. Further, we propose a model of the device band structure to explain the invariance of the energy selective quenching to bias polarity.