Silicon micromachining technology provides a cheap, massproduceable means to manufacture simple, low power consumption integrated metal oxide thin film gas sensors for industrial, environmental and medical purposes. Small size, low power consumption, low noise, low manufacturing cost, fast response time, long term stability under harsh conditions such as high temperature and aggressive gas atmospheres, as well as high selectivity are the basic requirements for the new micromachined gas sensor developed in this paper. The developed semiconductor gas sensor can be fabricated by the techniques that are compatible with IC fabrication. According the results of thermal simulation of the present gas sensor, the thermal isolation structure can work effectively. Uniform temperature distribution can be obtained while heating the suspended membrane. The supporting bridges can resist the heat transfer from membrane to silicon frame effectively. In the meantime, the heating response is very fast, and the power consumption is below 10 mW at the operating temperature of 300 centigrade.