Heat transfer in microfluidic devices and hence miniaturized thermal sensors has been widely analyzed in the last decade and is of great importance in applications such as micro-heat exchangers and microreactors. Here we report on some improvements in temperature measurement techniques, which can be the source of large errors due to their intrusiveness and the unreliability of conventional miniaturized thermal sensors. Gold thin films were deposited on a borosilicate substrate to create a low-cost, less intrusive 2D heat flux and temperature sensor for heat-transfer measurement along the main flow and within a microchannel. The performance of the new device for the thermal analysis inside a microreactor is illustrated with a neutralization reaction. The global heat flux released by the exothermal reaction is measured as a function of the flow rate and the reaction enthalpy is deduced. For a well studied acid-base reaction, the reaction enthalpy measured using this new heat-flux sensor had only a 5% discrepancy with the standard value, showing the efficiency of the new thin-film device. (c) 2013 Elsevier Ltd. All rights reserved.