NOVELTY - Manufacture of a thin-film gas sensor (100) provided with a pair of sensing electrode layers (51) on an electric-insulation layer, a gas sensitive layer (52) provided between the sensing electrode layers, and a gas selective-combustion layer (53) provided on the surface of gas sensitive layer, involves an annealing process. The annealing process removes gas containing hydrogen as main component from silicon-nitride layer (22) and silica layer (23) formed by chemical vapor deposition, after formation of the heat-insulating support layer (2).    USE - Manufacture of thin-film gas sensor used in domestic gas-leakage alarm units for sensing carbon monoxide, methane gas, propane gas, or ethanol vapors.    ADVANTAGE - The method reliably carries out degassing of support layer, which prevents emission of gas during baking of gas selective-combustion layer. Generation of swelling and peeling is prevented. The obtained sensor has excellent film strength and crack resistance.    DETAILED DESCRIPTION - Manufacture of a thin-film gas sensor provided with a pair of sensing electrode layers on an electric-insulation layer, a gas sensitive layer provided between the sensing electrode layers, and a gas selective-combustion layer provided on the surface of gas sensitive layer, involves an annealing process. The annealing process removes gas containing hydrogen as main component from silicon-nitride layer and silica layer formed by chemical vapor deposition, after formation of the heat-insulating support layer. The gas sensor consists of a silicon substrate (1) having a through-hole, with the opening of through-hole being spread and made into a diaphragm, a heat-insulating support layer, a thin-film-like heater layer (3) provided on the support layer, and an electric-insulation layer (4) provided to cover the support layer and heater layer. The support layer has a triple-layer structure of thermal oxidation layer (21), silicon-nitride layer formed by chemical vapor deposition, and silica layer formed by chemical vapor deposition.    DESCRIPTION OF DRAWING(S) - The drawing shows a longitudinal cross-sectional view of the thin-film gas sensor. (Drawing includes non-English language text)    Silicon substrate (1)    Support layer (2)    Heater layer (3)    Electric-insulation layer (4)    Thermal oxidation layer (21)    Silicon-nitride layer (22)    Silica layer (23)    Sensing electrode layer (51)    Gas sensitive layer (52)    Gas selective-combustion layer (53)    Thin-film gas sensor (100)