The aim of the present thesis is the development of a novel CO2 sensor, which is able to meet the main requirements for implementation in battery-powered electronic devices: high accuracy, fast response, negligible production costs, smallfootprint packaging, and low power consumption. In order to meet these requirements, the feasibility of an "electrolyte-gated transistor (EGT)" as CO2 sensor was investigated. The novel EGT-based sensor concept exploits synergies of various sensing techniques: the sensitivity of field-effect transistors (FET), the selectivity and modest power demand of electrochemical sensors and the ease of integration and operation of chemiresistors. An additional advantage of the investigated approach is the availability of wellknown and scalable production technologies (e.g., MEMS transducer), which allow miniaturization. The investigated EGT approach comprises a n-type semiconducting metal oxide (MOX) as channel and an ionic liquid (IL) as electrolyte. Such an approach for CO2 detection has not been described in literature yet. Therefore, the focus of the present thesis was to elucidate the underlying sensing mechanism. In this respect, experimental data as well as simulations were taken into account.