The development of portable, low cost, low power and high performance gas sensing systems based on MOX gas sensors involves advances in three areas: chemical sensors, data analysis algorithms or information extraction methods and electronic circuits to interface the sensors with the data processor. Currently, several data analysis algorithms and operation modes of MOX gas sensors have been developed and are being tested to improve their poor selectivity and stability of such sensors. However, to attain a practical high accuracy gas sensing system, it is also necessary to develop a high accuracy interface circuit. Furthermore, for sensor network applications, the interface circuit needs to have low power consumption and low cost. This thesis proposes circuit topologies to implement CMOS interface circuits for resistive chemical sensors. Specifically a general topology is proposed for the readout circuit that not only handles a wide dynamic range of resistance variation but also allows to implement resistance to period converters robust to supply and environment temperature variations. Furthermore, a flexible temperature control system is presented that enables handling heaters with different requirements in power consumption to achieve the desired operating temperature of the sensor. The simplicity and flexibility of the proposed topologies can facilitate the interface circuit implementation to different technology nodes. The proposed readouts and temperature control circuits were implemented in an 180nm CMOS technology. One the one hand, five Resistance-to-Period Converters (RTC) based on first order relaxation oscillators were designed. The circuits were tested with ±10% of variations in supply voltage and a range of environment temperature from 3 to 95◦C. Experimental results showed that the proposed topology can get robust RTCs to temperature and supply voltage variations without accuracy biasing circuits or high-performance sub-circuits, maintaining deviations in the output signal in the order of ±1% in almost two decades of resistance variations. On the other hand, a temperature control circuit based on the on/off control technique was also designed. The functionality of the control circuit was tested using the commercial AS-MLC gas sensor. Experimental results showed a resolution of ±4.5◦C in the operating temperature control.