Semiconductor-bimetallic ZnO-Ag-Cu (ZAC) heterojunction of different compositions were fabricated as highly sensitive SERS substrates. ZnO nanorods were synthesized using a facile hydrothermal route. ZAC composites were synthesized via impregnation method by keeping ZnO content same and varying the mole fractions of Ag and Cu. The ZnO matrix, known for its stability and photocatalytic properties, was decorated with Ag and Cu nanoparticles to enhance plasmonic activity and boost SERS. Introducing semiconductor oxide as SERS substrate reduces the substrate cost due to its self-cleaning property upon exposure to UV light. When SERS activity of ZAC composites were compared with either ZnO-Ag (ZA) or ZnO-Cu (ZC) composites, the best SERS performance was recorded with ZAC55, where the Ag and Cu content are same. ZAC55 produced a SERS enhancement factor of 6.2×10⁶ and a limit of detection of 10