Thermal sensors have applications in various areas of science and engineering for detection, measurement, observation and control of radiation. The basic elements of these sensors are the absorbing layer and the thin film battery of thermocouples that measures the temperature difference between this layer and the ambient. At present, such sensors can be manufactured by the micro machining process. The essential feature of these sensors is a very thin silica substrate layer. In designing the sensor, the properties of all the layers must be taken into account for optimization of its structure. The sensors detectivity is controlled by the figure of merit of the thermoelectric layer. PbTe is well known material that has found widespread applications in thermoelectric devices. PbTe based materials display unique properties, which are used for optimization of the figure of merit of n- and p-type thermoelectric layers. A simulation model for estimating the characteristics of the film thermoelectric sensor was presented. It was shown Volt-Watt sensitivity is ≈ 350 V/W for a sensor based on PbTe thermoelectric battery deposited on thin SiO2 layer (thickness ≈ 1μm). The construction of this sensor can be realized in MEMS design using a Si substrate.