We present a study of the thermal characteristics of an infrared detector (un-cooled micro-bolometer), based on an amorphous silicon germanium film (a-SixGey:H), deposited by plasma at low temperature (~ 300 ºC) and compatible with the standard CMOS technology. These films have been studied due to their high performance characteristics as high activation energy (Ea≈ 0.37 eV), high temperature coefficient of resistance (TCR≈ -0.047 K-1) and moderate room temperature conductivity (σRT≈ 2x10-5 Ω cm), which provides a moderate pixel resistance (Rcell≈3.5x108Ω). We have used two simple methods to calculate the thermal characteristics of the microbolometer. The thermal conductance (Gth) has been obtained from the electrical I(U) characteristics in the range where self heating due to bias is not presented. The temperature dependence of the electrical resistance and as well the temperature dependence of the thermal resistance have been obtained by measuring the I(U) characteristics in the device at different temperature values. Finally the results of both methods have been compared.