Metal-insulator-semiconductor (MIS) structures have been widely used in Si-based solar water-splitting photoelectrodes to protect the Si layer from corrosion. Typically, there is a tradeoff between efficiency and stability when optimizing insulator thickness. Moreover, lithographic patterning is often required for fabricating MIS photoelectrodes. In this study, we demonstrate improved Si-based MIS photoanodes with thick insulating layers fabricated using thin-film reactions to create localized conduction paths through the insulator and electrodeposition to form metal catalyst islands. These fabrication approaches are low-cost and highly scalable, and yielded MIS photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p+n-Si buried junction, further improved oxygen evolution reaction (OER) performance was achieved with an onset potential of 0.7 V versus RHE and saturation current density of 32 mA/cm2. Moreover, in stability testing in 1M KOH aqueous solution, a constant photocurrent density of ~ 22 mA/cm2 was maintained at 1.3 V versus RHE for 7 days.