In this paper, the synthesis of ZnO nanorods on a glass substrate using a hydrothermal method is described. First, spin coating was used to prepare a ZnO seed layer on a glass substrate. Then, hydrothermal synthesis was performed using a 0.03 M solution of Zn(CH3COO)2-2H2O, CH3OCH2CH2OH, and C2H7N and different synthesis times (30, 45, and 60 min) to synthesize ZnO nanorods on the ZnO seed layer. To improve the detection efficiency of both H2 and CO, a 5-nm-thick aluminum layer was deposited on the surfaces of the synthesized ZnO nanorods by thermal evaporation. To create a metal–semiconductor–metal gas sensor, 350-nm-thick interdigitated aluminum electrodes were deposited on the ZnO nanorods. The thus-obtained sensor was used to measure the concentrations of H2 and CO at temperatures ranging from 50 to 300 ℃ and at concentrations ranging from 100 to 2000 ppm. We compared the measurement results for pure and Al-decorated ZnO nanorods to determine the optimum sensing parameters. The measurement results showed the enhancements of the sensing efficiencies of H2 and CO when Al was used to decorate ZnO nanorods.