Abstract <p>In this work, a novel approach has been implemented to effectively enhance the performance of the CO gas sensor utilizing a bifacial porous silicon layer (B-PSi) with tri-metallic nanoparticles. The B-PSi was synthesized by double beam laser-induced etching (D-LIE) of the n-type silicon substrate by two like diode laser beams with a laser wavelength of 533 nm and a power of 30 mW. The tri-metallic, core/shell Au, Ag and Pd nanoparticles were incorporated on B-PSi through a dipping process in a solution of 1 : 1 : 1 mixing volumetric ratio of HAuC_l4, AgNO₃ and PdC_l2 with concentrations of 2 mM for 4 min. The performance of the B-PSi sensor was investigated using effective and non-poisonous measuring techniques involving the resonance frequency shift as a function of CO gas concentrations. The two structures with and without tri-metallic nanoparticles involving Al/(Ag : Au : Pd-NPs)/PSi/c-Si/PSi/(Ag : Au : Pd-NPs)/Al and Al/PSi/c-Si/PSi/Al were synthesised and tested at room temperature. Current-frequency properties are a function of CO gas concentrations presented an outstanding response of the B-PSi sensor with tri-metallic compared to the bare B-PSi sensor. A significant improvement in terms of gas sensitivity which is about 180.3%, is achieved at a gas concentration of 0.8 ppm. Further, the stability of the B-PSi sensor with tri-metallic has trebled over compared with the bare B-PSi gas sensor. The substantial enhancement of the B-PSi gas sensor with tri-metallic performance is attributable to the incorporated tri-metallic nanoparticles.</p>