The anodic polarizations of p-Si with various doping levels in concentrated HF solution have been studied. A theoretical model, based on the potential distribution during anodization, is developed. The computed polarization curves fit the experimental data quite well. Both the space charge region and the Helmholtz interface control the anodic behavior of p-Si. The effect of the Helmholtz interface becomes dominant as the doping level increases. The most likely dissolution mechanism during porous silicon formation involves the capture of two holes to form Si(II), which further reacts with protons to produce Si(IV) and H-2 gas.