This paper presents a monolithic chemical gas sensor system fabricated in industrial CMOS- technology combined with post-CMOS micromachining. The system comprises metal -oxide-covered (SnO2) micro-hotplates and the necessary driving and signal-conditioning circuitry. The SnO2 sensitive layer is operated at temperatures between 200 and 350◦C. The on-chip temperature controller regulates the temperature of the membrane up to 350◦C with a resolution of 0.5◦C. A special heater-design was developed in order to achieve membrane temperatures up to 350◦C with 5 V supply voltage. The heater design also ensures a homogeneous temperature distribution over the heated area of the hotplate (1–2% maximum temperature fluctuation). Temperature sensors, on- and off-membrane (near the circuitry), show an excellent thermal isolation between the heated membrane area and the circuitry-area on the bulk chip (chip temperature rises by max 6◦C at 350◦C membrane temperature). A logarithmic converter was
