Semiconductor gas sensors have some characteristic properties (Carotta et al. 2007) that, to some extent, determine the way and range of their use. The output signal of semiconductor sensors manufactured using the technology of thin layers from various active materials (for instance SnO 2 ) depends on the concentration of measured gas, and this dependency is non-linear (Nakata et al. 2001). However, at the same time, the output signal of the sensor is also subject to some other outside influences such as temperature and, in particular, humidity of the measured gas. The principle of a semiconductor sensor with surface adsorption activity is based on the exchange of electrons caused by gas adsorption in active layer of the oxide and is based on the stripe model of the semiconductor (Henrich, Cox 1996). If semiconductor of type n and reduction gas (i.e. also NH 3 ) is considered, the presence of reduction gas leads to the decrease of specific resistance of the active layer and conductivity increases. With regard to the nature of semiconductor material (a metal oxide) and work- The paper deals with continuous monitoring of NH 3 desorption from material used as bedding in animal breeding establishments, using five semiconductor sensors SP-53 (FIS Inc.). In lab experiments, two groups of sensors from two categories, to which the manufacturer divided the sensors based on the value of their resistance R S , were used. Also the influence of air humidity over the values of NH 3 concentrations measured by individual sensors was monitored. The study ascertained statistically relevant differences between NH 3 concentration values measured by both groups of sensors, in the range from 8.5% to 23.1%. The biggest differences were confirmed for relative air humidity around 85%. It was verified that setting a convenient value of the load resistance R L with regard to the R S of each sensor, along with the selection of limited range of measured temperatures and relative air humidity, leads to satisfactory correction of the sensor output data, regardless of the division of sensors in categories pursuant to the value of their resistance in manufacturing.