A method of sensing the amount of a gas in a fluid flow includes operating an acoustic wave (AW) sensor at a first resonant frequency. The AW sensor includes a high temperature stable piezoelectric plate coupled to a first gas-absorbing layer. Also included is combining a fluid flow having a gas component with the first gas-absorbing layer at a temperature of at least about 500.degree. C. At least one resonant frequency of the AW sensor is sensed. The amount of gas in the fluid flow is sensed by correlating the resonant frequency with the amount of gas absorbed in the first gas-absorbing layer.A sensor for sensing the amount of a gas in a fluid flow includes a first gas-absorbing layer, a high-temperature-stable piezoelectric plate coupled to the first gas-absorbing layer, and a controller coupled to the high-temperature-stable piezoelectric plate. The controller is coupled to the high-temperature stable piezoelectric plate to measure a resonant frequency in the high temperature stable piezoelectric plate correlated with an amount of gas absorbed by the first gas absorbing layer, whereby the amount of a gas in a fluid flow is sensed. The high-temperature-stable piezoelectric plate is formed of at least one material selected from the group consisting of AlN, GaN, Al.sub.1-xGa.sub.xN (0.ltoreq.x.ltoreq.1), GaPO.sub.4, AlPO.sub.4, and materials having the crystal structure of Ca.sub.2Ga.sub.2Ge.sub.4SiO.sub.14, e.g., Ca.sub.2Ga.sub.2Ge.sub.4SiO.sub.14, La.sub.3Ga.sub.5SiO.sub.14, La.sub.3Ga.sub.5.5Nb.sub.0.5O.sub.14, La.sub.3Ga.sub.5.5Ta.sub.0.5O.sub.14, and the like.