In aseptic filling systems, hydrogen peroxide vapour is commonly used for the reduction of microbial contaminations in carton packages. In this process, the germicidal efficiency of the vapour depends especially on the H2O2 concentration. To monitor the H2O2 concentration, a calorimetric H2O2 gas sensor based on a catalytically activated thin‐film thermopile is investigated. Two different sensor layouts, namely a circular and a linear form, as well as two various material pairs such as tungsten/nickel and gold/nickel, have been examined for the realization of a thin‐film thermopile. Additionally, manganese oxide and palladium particles have been compared as responsive catalysts towards H2O2. The thin‐film sensors have been investigated at various H2O2 concentrations, gas temperatures and flow rates.