We present fabrication and performance of a free-standing thermoelectric and catalytic hydrogen gas sensor. The response of the device to hydrogen gas is reported at different operating temperatures and hydrogen concentrations. The response of the free-standing device is also compared to the devices built with either a single large membrane or two membranes. At an operating temperature of 100 °C, the free-standing type device shows the voltage response twice as high as those of the membrane type devices. The results show that the thermal differential in the thermoelectric film of the free-standing type device is greatly enhanced as the heat diffusion through the membrane is prohibited. The free-standing type device shows good stability above 60 °C and is selective for hydrogen against methane and propane gases.