The photoelectrochemical performance of Si photoanode with a metal–insulator–semiconductor (MIS) structure is limited by weak Schottky barrier and poor charge transfer. In this work, a MIS structure, n-Si|dispersed NiSi_x/NiO_x patches|Au nanoparticles, is designed for efficient water oxidization with high stability. The photoanode exhibits a high activity with a low onset potential of ∼0.88 V and a high photocurrent density of ∼34 mA/cm² at 1.23 V versus reversible hydrogen electrode (RHE), and retains excellent stability in 1.0 M NaOH for ∼10 h. We find that the improved photovoltage is contributed by the strengthened pinch-off effect of inhomogeneous Schottky barriers induced by the synergistic effect of decreased Schottky barrier height difference and increased depletion width in n-Si. We show that the enhanced photocurrent attributes to the reduced hole transport resistance by introducing high-conductive NiSi_x and Au-NP bridge layers. Our findings demonstrate a promising strategy for the development of highly efficient and stable Si-based photoelectrodes for water oxidization.