Transient x-ray spectroscopy has become a powerful tool for photoelectrochemistry. X-rays can measure the coupled electronic and structural dynamics that underlie excited state polaron formation, molecular reaction dynamics, and hot carrier thermalization pathways. Element-specific responses can be used to measure electron or hole transport between each component of a photoelectrode (i.e. light absorber, oxide protection layer, catalyst). In this talk, we discuss how improvements in the signal to noise ratio of our transient XUV spectrometer now allow for the measurement of mid-gap and surface state filling dynamics. The energy of electrons and holes as a function of time is measured for a ZnTe photocathode. The thermalization, mid-gap state filling, and recombination are measured in terms of the energies of electrons and holes. An ab-initio approach using the Bethe-Salpeter equation with time-dependent electron and phonon populations is used to predict and confirm the transient XUV measurements. The few nanometer surface sensitivity of grazing angle, transient XUV measurements make it favorable for measuring interfaces in photoelectrochemistry.