A photoanode exhibiting high water-splitting efficiency at low bias potential is essential for stand-alone water-splitting devices through a tandem system combined with a photovoltaic device. However, many previous studies employing a typical BiVO₄/WO₃ heterojunctions focused on water oxidation at the maximum thermodynamic water splitting potential, 1.23 V vs. the reversible hydrogen electrode (V_RHE). Here, we suggest a strategy for high water oxidation efficiency at low potential using 3D BiVO₄/ZnO heterojunction photoanodes. The BiVO₄/ZnO heterojunction exhibits a lower onset potential compared to the commonly used WO₃ heterojunction. Due to the 3D ordered structure, the BiVO₄/ZnO achieves enhanced light harvesting efficiency and improve charge separation efficiency at low bias potential by ZnO heterojunction. As a result, the BiVO₄/ZnO photoanode exhibits a water-splitting photocurrent density of 3.3 ± 0.2 mA /cm² is obtained at 0.6 V_RHE under 1 sun illumination.