In situ photovoltage (PV) and photoluminescence (PL) are used to obtain information about the band bending of Si and the PL quenching by nonradiative (nr) surface recombination during electrochemical treatments of silicon in aqueous fluoride solutions. The onset of the porous silicon formation in diluted NH4F solution is accompanied by a decrease of nr surface recombination. Intensive electrochemical etching leads to an increase of nr surface recombination, to positively charged surface states, and to a strong increase of the current density. The increase of the current density is higher than expected for an ideality factor of 1, which gives evidence for a decrease of the effective barrier height during porous silicon formation. The evolution of hydrogen and its penetration into near surface regions lead to the formation of nr surface defects. The lowest nr surface recombination in the regime of porous silicon formation has been observed in higher concentrated HF solution even at high current densities. Therefore, the intermediates of the reactions which lead to pore formation are more of an ionic nature than like Si dangling bonds. Negatively polarized intermediate states (charged species or dipoles) arise when the electrolyte reaches the Si surfaces during the etchback of oxide layers.