Achieving stable operation of high efficiency photoanodes used as components of solar water splitting devices is critical to realizing the promise of this renewable energy technology. Here, we show that a p-type transparent conducting oxide (p-TCO) can function as a selective hole conduct and corrosion protection layer on photoanodes used for light-driven water oxidation. We selected NiCo₂O₄ with the inverse spinel structure was used as the p-TCO and show that this material, when integrated with Si-based photoanodes, has the requisite electronic structure, stability, transparency, and hole conductivity to achieve sustained and efficient solar water oxidation. NiCo₂O₄ was deposited on n-Si (100) and np-Si (100) by reactive sputtering at a substrate temperature of 70-100 °C. The film structure was amorphous, as shown by the lack of XRD and Raman features. P-type conductivity was confirmed by measurement of a positive Seebeck coefficient. Light transparency of >70% (l > 400 nm) was achieved with a NiCo₂O₄ thickness of 40 nm. The hole conductivity was 50-60 S/cm and, as expected, p-NiCo₂O₄ forms a rectifying contact to n-Si. Photoelectrochemical (PEC) evaluation was performed in aqueous 1M NaOH (pH 14) with simulated AM1.5 illumination; these conditions would rapidly corrode the n-Si photoanodes in the absence of a protection layer. PEC performance of the np-Si/p-NiCo₂O₄ structures is excellent, particularly when a thin NiFe oxygen evolving catalyst is applied. An onset potential of 0.95 V vs. RHE is observed, which is one of the lowest reported for a Si-based photoanode. The current density at the reversible potential for water oxidation (+1.23 V vs. RHE) is >25 mA cm^-2, and the current rises to a limiting value of 30 mA cm^-2 at more anodic potentials, which demonstrates the attractive combination of transparency and low-resistance hole conductivity in the NiCo₂O₄. Long-term testing indicates multi-day stability with minimal decrease in performance or observable corrosion of the Si photoanode. In depth characterization of both the solid-solid interfaces between NiCo₂O₄ and light absorber/catalyst and of the solid/electrolyte interface will be discussed. This work demonstrates that p-TCOs are promising as corrosion protection layers for stable water oxidation photoanodes. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.