A microhotplate is a sensor platform that is a multilayered, suspended structure manufactured and micromachined from a silicon wafer. The structure consists of an integrated heater, heat distribution plate, and surface electrodes, all separated by electrically insulating layers. A semiconducting metal-oxide sensing film is deposited on the surface electrodes after micromachining and packaging. Microhotplates have been used for detecting and identifying gases such as chemical warfare agents using temperature-programming methods. In these methods, gas selectivity is due to relative reaction kinetics and surface intermediate species, and improving these techniques requires a fundamental understanding of these mechanisms. Therefore, we have developed a technique, using a microhotplate as a surface science tool, to measure the desorption energy of an analyte on a microhotplate gas sensor. The isothermal desorption technique takes advantage of the microhotplate's rapid heating characteristics (>10⁶ K/s) to compensate for the extremely small surface area, and a model is developed to account for both the response of the sensor and of the vacuum system. Results of benzoic acid desorption from tin oxide are modeled as a first-order process, and the kinetic rate constants, viz. the pre-exponential factor and the desorption energy, are determined to be 1 x 10¹⁷ s^-1 and 97 kJ/mol respectively. Background on microhotplate gas sensors, basic principles of conductometric metal oxide sensors and temperature programmed sensing will be reviewed, and the qualitative influence of various rate parameters on the desorption model will be discussed.