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Developing efficient semiconductor photoanodes demonstrating strong light absorption, efficient separation of photogenerated charge carriers, and reduced charge carrier recombination rate can benefit PEC water splitting. Integrating a wide band gap semiconductor with narrow bandgap material with suitable band alignment can enhance PEC performance. Herein, we have fabricated novel MoO3/γ-In2Se3 heterostructure photoanodes using RF magnetron sputtering. The films structural, optical, morphological, and elemental composition were investigated in detail using low-angle XRD, Raman spectroscopy, XPS analysis, EDAX, and FESEM. The XRD, Raman, XPS, and EDAX results strongly confirmed the presence of desired phases of MoO3 and γ-In2Se3 layers in heterostructure without forming any impurity or alloy. FESEM micrographs revealed a uniform, dense grain structure. Optical analysis of MoO3/γ-In2Se3 done by UV–Visible spectroscopy shows increased absorption compared to pristine-MoO3. Conduction and valence band-edge potential values indicate that MoO3/γ-In2Se3 films are suitable for PEC hydrogen production. The PEC performance of these heterostructure photoanodes was evaluated by performing LSV, Chronoamperometry, EIS, and Mott–Schottky analysis. LSV results of MoO3/γ-In2Se3 showed a 10-fold increase in photocurrent density and attained higher photoconversion efficiency (0.5%) compared to pristine-MoO3 photoanode. EIS analysis revealed that MoO3/γ-In2Se3 photoanodes had small charge transfer resistance. Investigation of Mott Schottky results shows carrier density increases from 2.8 × 1019 cm−3 to 2.1 × 1020 cm−3 after incorporating γ-In2Se3 over MoO3. An increase in time-dependent photocurrent density reveals that MoO3/γ-In2Se3 films have effective electron-hole separation. Our finding suggests that MoO3/γ-In2Se3-based heterostructure photoanode can enhance light harvesting capacity and suppresses carrier recombination rate, eventually boosting PEC performance. Moreover, these results encourage the development of highly efficient photoelectrodes based on heterostructures for solar water-splitting applications. [ABSTRACT FROM AUTHOR]