Ammonia decomposition, a process converting 2NH3 into N2 and 3H2, presents a solution for hydrogen storage and distribution challenges due to its high storage density and ease of liquefaction. The article discusses the utilization of gallium nitride nanowires (GaN NWs) on silicon wafers as a semiconductor platform for solar-driven ammonia decomposition. By combining ruthenium nanoparticles (Ru NPs) with GaN NWs/Si, a photo-thermal-coupled catalytic architecture is developed, showing a substantial reduction in activation energy for NH3 decomposition. The hybrid architecture achieved a high hydrogen evolution rate and long-term stability, making it a promising system for on-site hydrogen generation. Operando spectroscopic and computational analyses highlighted the efficient charge carriers' management and enhanced catalytic activity. The study demonstrated the successful conversion of ammonia to hydrogen under sunlight, with the architecture's viability validated through outdoor tests. This innovative approach opens avenues to efficient hydrogen production through ammonia decomposition, leveraging the synergistic effects of GaN nanowires, silicon, and ruthenium for sustainable energy solutions.