Achieving stable operation of photoanodes used as components of solar water splitting devices is critical to realizing the promise of this renewable energy technology. It is shown that p-type transparent conducting oxides (p-TCOs) can function both as a selective hole contact and corrosion protection layer for photoanodes used in light-driven water oxidation. Using NiCo2O4 as the p-TCO and n-type Si as a prototypical light ab-sorber, a rectifying heterojunction capable of light driven water oxidation was created. By placing the charge separating junction in the Si using a np+ structure and by incorporating a highly active heterogeneous Ni-Fe oxygen evolution catalyst, efficient light-driven water oxidation can be achieved. In this structure, oxygen evolution under AM1.5G illumination occurs at 0.95 V vs. RHE and the current density at the reversible potential for water oxidation (1.23 V vs. RHE) is >25 mA cm-2. Stable operation was confirmed by observing a constant current density over 72 hours and by sensitive measurements of corrosion products in the electrolyte. In-situ Raman spectroscopy was employed to investigate structur-al transformation of NiCo2O4 during electrochemical oxidation. The interface between the light absorber and p-TCO is crucial to produce selective hole conduction to the surface under illumination. For example, annealing to produce more crystalline NiCo2O4 produces only small changes in its hole conductivity, while a thicker SiOx layer is formed at the n-Si/p-NiCo2O4 interface, greatly reducing the PEC performance. The generality of the p-TCO protection approach is demonstrated by multi-hour, stable, water oxidation with n-InP/p-NiCo2O4 heterojunc-tion photoanodes.