MOS gas sensor arrays based on MEMS gas sensor platforms were developed for the detection of carbon monoxide (CO), nitrogen oxides (NOx) and ammonia (NH3), and their gas sensing characteristics in binary mixed-gas system were investigated. Three gas sensing materials with nano-sized particles for these target gases, Pd-SnO2 for CO, In2O3 for NOx and Ru-WO3 for NH3 were synthesized using a sol gel method. All the sensors showed good properties for their target gases at the optimum points for micro-heater operation. From the experimental data in MEMS gas sensor arrays in a binary mixed system, the gas sensing behavior and sensor response in mixed gas systems were scrutinized. The gas sensing behaviors to the mixed gas systems suggested that specific adsorption and selective activation of adsorption sites might occur in gas mixtures and offer the priority for the adsorption of specific gas. Thorough analysis of the sensing performance of the sensor arrays will make it possible to discriminate the components in gas mixtures as well as their concentrations. (C) 2012 Elsevier B.V. All rights reserved.