In this paper, a ZnO seed layer was deposited by spin coating on sapphire templates with patterned concave arrays used as substrates. Then, a hydrothermal method was used with a 0.03 M solution of Zn(CH3COO)2‧2H2O, CH3OCH2CH2OH, and C2H7NO to synthesize ZnO nanorod arrays on the surface of the ZnO seed layer at different synthesis times (30, 45, and 60 min). To evaluate the effect of Cu metal on enhancing the H2 and CO gas sensing of the ZnO nanorods, the samples were divided into two groups: ZnO nanorod arrays without and with Cu decoration. We compared the photoluminescence properties of the arrays synthesized for the above durations, as well as those synthesized for 60 min both with and without Cu decoration. All ZnO nanorod arrays exhibited a distinct emission peak in the UV region at approximately 378 nm. However, the emission intensity of the ZnO nanorod arrays decorated with Cu was significantly higher than that of the undecorated nanorods. To fabricate a metal–semiconductor–metal gas sensor, we deposited 350-nm-thick interdigitated Cu electrodes on the ZnO nanorod arrays. The sensor was utilized to measure the concentrations of H2 and CO across ranges of temperatures and concentrations (100 to 2000 ppm). We identified the optimal sensing parameters by comparing the results obtained from the ZnO nanorod arrays synthesized for 60 min with and without Cu decoration.