A temperature control system for integrated resistive gas sensor arrays is proposed. The circuit is a part of a portable system for ambient gas monitoring formed by a sensor array, the IC front-end, the temperature control system with the heater and the pattern recognition algorithm for the processing of the acquired data from the front-end. The sensors are arranged in order to detect a particular kind of gas among which CO2, CH4, H2 and SO2, through a 4-channel read-out front-end able to furnish the digital output signal. The temperature control is simplified by the presence of a second resistance matched with the sensor that operates as a thermal sensor. In this manner it is possible to control the sensor temperature without interference. The problem of the temperature control of the heater is reduced to the control of a resistance. The current (more generally the power) delivered to the heater resistance must be such that the temperature has to remain constant. This task is demanded to the second resistance, close to the heater one, that remains at the same temperature. Typically, such kinds of controls are implemented by topologies that maintain current sources or heater currents constant. In this work, the control circuit is able to maintain the power delivered to the heater resistance as constant.