This chapter delves into rapid development of semiconductor nanomaterials in photocatalysis, mainly focusing on its pivotal role in water splitting for hydrogen generation. Continuous global energy demand and the imperative shift towards sustainable energy sources, innovative technologies like photocatalysis offer promising solutions. By utilizing photon energy, semiconductor photocatalysts facilitate the decomposition of water into oxygen and hydrogen gas, presenting a clean and renewable fuel source with widespread applicability across transportation, manufacturing industry, and electricity generation sectors. The study provides a depth exploration of the foundation principles underpinning photocatalysis, presenting a comprehensive grasp of the complex mechanisms. In addition, deep exploration on how semiconductor materials absorb photons, initiating the generation of electron–hole pairs, and catalyze redox reactions were discussed. These reactions ultimately lead to the production of hydrogen and oxygen gas, unraveling the intricate pathways through semiconductor nanomaterials, which drive the process of water splitting. By scrutinizing both the challenges and opportunities inherent in the water-splitting process, this study sheds light on the transformative capacity of semiconductor nanomaterials to reshape the renewable energy towards sustainability and mitigate the deleterious effects of climate change. Findings from this study not only advancing clean energy technologies but also offer potential for large-scale hydrogen production through semiconductor photocatalysis and aim to drive technological advancements in semiconductor photocatalysts, facilitating progress towards a greener future.