The intensification of fast exothermic reactions can be achieved by using microstructured reactors (MSR) which provide improved mass & heat transfer rates leading to higher overall reaction kinetics. But for highly exothermic reactions the heat evacuation becomes not efficient enough and unwanted hot spots are formed. In this study, first the mixing in MSR is quantified for different geometries and then temperature profiles are measured using a novel quantitative IR-thermometry method. The results are fitted to a lumped parameter model of overall reaction kinetics and the influence of the operating conditions is established.