Hydrogen gas is widely used in a variety of industries, for example in the chemical industry used in the process of ammonia production and refining of hydrocarbons also used in petroleum industries, nuclear reactors, and fuel cells. Hydrogen gas has a low minimum ignition energy (0.017 mJ) and high heat of combustion (142 kJ/g) and has a wide flammable range (4-75%). It is a colorless and odorless gas, which reveals the need for a suitable sensor to detect hydrogen. So far, various methods for hydrogen gas sensing have been proposed, including thermal conductivity, electrochemical, resistive based, mechanical, acoustic and optical methods. In recent years, semiconductor metal oxides have been one of the options considered for gas sensing applications. These sensors are mainly divided into resistive and gasochromic categories, in which the latter is classified as an optical sensor. In this study, a thin film of molybdenum oxide was deposited on the glass substrate by sputtering method and then palladium nanoparticles as a hydrogen sensing reaction catalyst, were decorated on MoO 3 thin film; moreover, as a new method in the optical sensing methods, a small halogen lamp was used as a substrate, which operates as a light source in the gas sensing process and simultaneously the heating agent for the Pd/MoO 3 sensing layer. To investigate the effect of temperature on the sensor layer, the samples were annealed at three temperatures of 100, 200 and 400 °C. The XRD test shows that the sample is in the amorphous phase after the deposition and goes to the ?-MoO 3 phase by annealing at 400 °C. Raman spectroscopy has been used to determine the structural properties of the material and UV-Visible spectroscopy has been used to investigate the optical properties of the material, which shows over 70% traarency for the samples. The sensing properties of this material were studied at room temperature using the same method. SEM microscopy images of the sample surface show a uniform, fine-grained, relatively compact surface. Also, the cross-sectional images of the samples show a thickness between 110-120 nm for the samples. Gas sensing tests show that the sensor is capable of sensing hydrogen gas at room temperature but performs best results at operating temperatures of 100 and 150 °C and the Pd/MoO 3 sensor is capable of detecting low gas concentrations (25 ppm) and has satisfying stability.