This work presents a robust method for whole chip temperature mapping in microfluidic devices using a photostable fluorescent-polymer thin film that can be incorporated during the bonding stage. Temperature measurements are based on the ratio of two bands in the fluorescence spectrum of N,N-bis(2,5-di-tertbutylphenyl)-3,4,9,10-perylenedi carboximide (BTBP) dye. Spectral bands were carefully chosen to minimize errors caused by photobleaching of the dye which results in a perceived drift in the temperature with time. The improvements result in a useful working time for this type of measurement to >20 h. We achieve a temperature resolution <2 °C with drift less than 0.58 °C h⁻¹ in thin-films of common polymers used in microfluidic device fabrication (polystyrene, polydimethylsiloxane, and polymethylmethacrylate) Finally, we demonstrate the usefulness of this technique by presenting examples of temperature fields mapped by the thin-films in several thermal microfluidic devices.