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A micromachined gas sensor based on a catalytic thick film/SnO 2 thin film bilayer and a thin film heater was investigated for CH 4 sensing. The sensor demonstrated good sensitivity and high selectivity with low power consumption. The thin film heater and the SnO 2 thin film sensing layer were deposited on a Si micromachined structure having a silicon oxide-silicon nitride membrane. On the SnO 2 sensing layer, a Pd-Al 2 O 3 catalytic thick film was formed to oxidize interfering gases selectively. The sensor realized low power consumption and fast thermal response due to the low thermal conductance and the small heat capacity of the membrane. The power consumption at an operating temperature of approximately 450 • C was 30 mW. The sensitivity (R air /R gas ) to 2000 ppm CH 4 in air was greater than 5, while the sensitivity to H 2 , an interfering gas, was relatively low.