Microstructured reactors (MSR) with characteristic dimensions below 100 μm are warranted to maintain close to isothermal conditions when carrying out quasi-instantaneous highly exothermic reactions. Unfortunately, such small dimensions increase the risk of clogging, create high pressure drop and are costly to number-up. The multi-injection (MI) MSR, where one of the reactants is added stepwise along the reactor length, allows working with larger dimensions (diameter >500 μm) while maintaining good temperature control. Herein presented MI-MSR is made of low temperature co-fired ceramics (LTCC) with herringbone mixing structure inside the reactor channels and is shown to mix efficiently in a large range of Reynolds numbers Re = 20–130. The cyclization of pseudoionone is studied as a model of a highly exothermic fast reaction. The temperature profiles are characterized by a quantitative infrared thermography. The developed LTCC MI-MSR allows ∼ 8-fold reduction of hot spot temperature as compared to the adiabatic temperature rise. Moreover, ∼500-fold intensification is achieved as compared to the conventional semi-batch process with reduced solvent mass by a factor of 2 while attaining a yield of target product above 98%.