Abstract: A semiconductor sensor for fluids comprised of a body composed of an inorganic semiconductor material which is provided with a drain and source zone interconnected by a channel zone and including a layer of a reactive organic material capable of forming a reversible bond with at least a portion of the fluid being detected in the vicinity of the channel zone between the source and drain zones. The reactive organic material, such as carotenoids, polypropylenes, phthalocyanines, etc. reversably interacts with molecules of a given fluid substance and produce a reversible change in the surface potential of the layer composed of the organic material via a field effect and thus produce a reversible change of resistance in the channel zone and indicates the presence of such fluid by a change in the drain current of the sensor.