Quasi-instantaneous exothermic reactions lead to the formation of unwanted hot spots even when carried out in conventional microstructured reactors (MSR) with tube diameter of 100 − 1000 μm. For this reason, alternative MSR designs are warranted to enable process intensification of fast reactions with characteristic reaction times < 1 s. The continuous multi-injection MSR, where one of the reactants is added to the main flow of reactants along reactor length, may improve temperature control. The latter was studied first theoretically using numerical simulations and then proved experimentally with the cyclisation of pseudoionone to α- and β-ionones as a model reaction. The multi-injection MSR made of low temperature co-fired ceramics led to an yield of α-ionone and β-ionone > 0.98 reaching a 500-fold process intensification as compared to the conventional semi-batch process. The temperature profiles monitored by quantitative infrared thermal imaging confirmed 8-fold reduced temperature rise as compared to an adiabatic operation, which was achieved by injecting one of the reactants at three different points.