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Here we report on novel high temperature gas sensors that have been fabricated using an SOI (silicon-on-insulator) -CMOS process and deep RIE back-etching. These sensors offer ultra-low power consumption, low unit cost, and excellent thermal stability. The highly-doped single crystal silicon (SCS) layer of a standard SOI-CMOS process, which is traditionally used to form the source and drain regions of a MOSFET, is used, for the first time, to form a resistive heater of a micro-hotplate in a high-temperature gas sensor. Our sensors have a power consumption of only 12-30 mW at a temperature of 500degC. We have observed that the drift in resistance of a SCS heater held at 500degC for 500 hours, without burn-in, was less than 1%. SCS micro-hotplates are not only suitable for chemoresistive sensors, as described here, but also calorimetric gas sensors that require these high operating temperatures. Tungsten oxide nanorods have been deposited onto our micro-hotplates by atmospheric chemical vapour deposition and have shown reasonable sensitivity to ethanol vapour in air.