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Safe deployment of hydrogen as a clean energy carrier demands gas sensors capable of detecting leaks at sub-ppm concentrations with fast response, low power consumption, and straightforward integration into process monitoring systems. Here we report a palladium nanoparticle-decorated Graphene/Silicon (Pd-G/Si) Schottky junction diode that addresses these requirements through a deliberate combination of reverse-bias operation and thermal activation near the Pd hydride dissociation temperature. Palladium nanoparticles serve as a chemical sensitizer. Operating under reverse bias at −0.8 V and 120°C – a temperature regime that maximizes PdHₓ formation kinetics without entering the hydride dissociation regime above ∼150°C – the device achieves a detection limit of 0.5 ppm with response and recovery times of 20 s and 90 s, respectively, at a bias-power consumption below 0.2 µW. Current-noise analysis confirms that the −0.8 V reverse bias minimizes current fluctuations and produces a white-noise-dominated low-frequency spectrum only moderately sensitive to temperature, preserving a favorable signal-to-noise ratio. Arrhenius analysis of the response and recovery kinetics yields PdHₓ dissociation energies consistent with those of dilute α-phase PdHₓ, corroborating the thermally controlled sensing mechanism. The sensing area is inherently miniaturized, confined to the narrow conduction channel at the graphene/Si edge, so that only a small fraction of the surface requires PdNP coverage, reducing fabrication cost relative to large-area architectures. The Pd-G/Si Schottky diode delivers sub-ppm H₂ detection through simple two-terminal current measurements without specialized instrumentation – establishing it as a promising, cost-effective platform for hydrogen safety monitoring in the ppm-to-ppb concentration range.