In this paper, the electrothermal model of a microelectromechanical (MEM) gas sensor is presented, as well as a simulation approach that computes the transient state electro-thermal behavior of MEM gas sensor and that it is compatible with the model used in discrete devices, using commercial circuit simulators (e.g., SPICE). Furthermore, the resulting values of the current magnitude, that it should be applied to the microhotplate (MHP) to reach the necessary level of temperature to activate the sensing mechanism, are presented. The results are based on the solution of the system of equations that governs the heat transport in the device.