In a chemi-resistive gas sensor, the sensing properties are essentially improved through surface functionalization. In the present work, silicon nanowalls (SiNWs) were carved on silicon wafers by metal-assisted chemical etching technique. Over the SiNWs, platinum (Pt) and palladium (Pd) nanoparticles were deposited through a fluoride-free galvanic displacement deposition technique. The surface-decorated SiNWs were then evaluated for their sensing behaviour towards hydrogen (H-2) gas. The morphological investigation revealed vertically aligned SiNW architecture with Pt and Pd nanoparticles sprinkled over the wall-tips. The crystallographic analysis indicated that the SiNWs has the original single-crystalline nature of the silicon wafer even after surface modification. Comparison of H-2 gas sensing efficacies indicates an similar to 8 and similar to 4-fold corresponding increase in Pd and Pt functionalized SiNWs, at 200 degrees C, with respect to pristine SiNWs. A plausible sensing mechanism is suggested with a suitable parallel resistance model. The combinatorial effect of single-crystalline SiNWs and catalytic properties of Pt and Pd resulted in enhanced sensing characteristics. Moreover, the economically scalable aptitude of the fabrication technique makes them suitable for real-time and facile industrial applications.