Abstract: The invention concerns a sensor for detecting and/or measuring concentration of electric charges contained in an atmosphere. The sensor comprises a field-effect transistor structure including a bridge, which forms a gate and is suspended above an active layer located between drain and source regions. A gate voltage having a specific value is applied on the bridge. A so-called air gap region is included between the bridge and the active layer or an insulating layer deposited on said active layer, and has a specific height. An electric field (E), defined as the ratio between the gate voltage and air gap height, is generated in the air gap. The electric field generated in the air gap has a value not less than a specific threshold, sufficiently important for the electric field (E) to influence the distribution of electric charges contained in the atmosphere and present in the air gap, and to enable high sensitivity of the sensor to be achieved through accumulation of the electric charges on the active layer.