Thick film thermistors based on spinel-type semiconducting oxide (Mn1.6Co0.8Ni0.35Ru0.25O4) were studied. On the basis of the structure analysis (SEM observations and x-ray investigations) the computer model of the thermistor was proposed. The model was created in two steps. First, the structure of the element was simulated by generating of the spinel-type particles at the glassy matrix. Next, the model of the real structure was converted to the resistive network consisting of nodes and bonds. Various types of the resistances were considered (crystallite/grain resistance of the oxide, boundary resistance between grains, glassy layer resistance between grains). As a result the effective resistances of the random network at the different temperatures were calculated using the voltage nodes method basing on the first Kirchhoff law. Additionally the ruthenium dioxide powder was considered as a modifier. This paper presents some experimental and theoretical results obtained from the proposed model.