This review paper discussed recent developments in and prospects of metal-insulator-semiconductor (MIS) nanojunctions for hydrogen evolution from water splitting in photoelectrochemical (PEC) cells. The basic principles of MIS that functionalise upon the critical intermediate ultrathin insulator layer in the sandwiched MIS structure are explained in detail, which is followed by a summary and discussion on the generalised approaches for synthesising MIS-based nanojunctions, including specific details on the preparation of metal, insulator and semiconductor layers. Key challenges associated with the application of MIS nanojunctions in semiconductor photocatalysts for water splitting are also addressed in addition to the technique s advantages and disadvantages. Recent developments of photovoltaic cell structures based on MIS principles are also reviewed because PEC cells are usually coupled with photovoltaic cells and electrolysers for enhanced efficiency in water splitting. Finally, the prospects of MIS nanojunctions for water-splitting applications in the context of addressing energy and environmental concerns are discussed.