The behavior of the quasi-Fermi levels of electrons and holes at various semiconductor/liquid interfaces has been probed through the use of thin, high purity, low dopant density single crystal Si photoelectrodes. Since standard Air Mass 1.5 illumination is sufficient to produce high level injection conditions in such samples, minimal electric fields can be present near the solid/liquid interface. Under these conditions, efficient charge separation relies on establishment of kinetic asymmetries at the back contacts while effectively sustaining photogenerated carrier concentration gradients in the photoelectrode. These conditions were achieved for Si/CH3OH interfaces in contact with the 1,1’-dimethylferrocene(+/0), cobaltocene(+/0), methyl viologen(2+/+), and decamethylferrocene(+/0) redox couples. For redox couples having energies near the top of the Si valence band, such as 1,1’-dimethylferrocene(+/0), the sample acted like an n-type photoelectrode, yielding large photovoltages for collection of electrons at the back contact and small photovoltages for collection of holes. For redox couples having energies near the bottom of the Si conduction band, such as cobaltocene(+/0), the sample acted like a p-type photoelectrode, yielding large photovoltages for collection of holes at the back contact and small photovoltages for collection of electrons.