Hydrogen sulfide (H2S) is an offensive-smelling, colorless, and toxic gas that can cause poisoning even in small quantities. In this study, we proposed a sensor that can detect H2S with a low composition using SnO2 and Au nanoparticles as a catalyst. We investigated the structure formed in the thin layer of a sensing material and determined whether it can absorb the tested gas well and produce a high sensing response. We also determined the optimal operating temperature and showed that it has excellent response and recovery times. Pure SnO2 was synthesized by a simple thermal decomposition method. In the next step, the wet chemical method was used to dissolve the SnO2 and Au nanoparticles before a viscous liquid compound was deposited onto the electrode by the drop-casting method. The sensor’s performance for H2S gas detection was tested at low concentrations with four concentrations of Au nanoparticles on SnO2-based materials. The results showed that the structure formed in the thin layer is an agglomeration of hollow grains, which allows the gas to be absorbed properly. The result indicated that 40 µl of Au nanoparticles was the optimum concentration for a H2S gas sensor, with responses of 65.12% at 0.2 ppm and 87.34% at 1 ppm. The response time was 8 s, whereas the recovery time was 31 s. Moreover, the optimal operating temperature for the reaction was 200 ℃. The findings of this experiment demonstrated that depositing Au-nanoparticle-decorated SnO2 by the drop-casting method produced a structure with superior gas-sensing performance.