Different volumetric flow rates and various reactor configurations were studied in order to characterise the flow-through plate microreactor. The reactor is fabricated in silicon microsystem technology. The investigations focus on the determination and modelling of the fractional conversion and the potential drop over the reactor surface. Both parameters are necessary to size electrochemical reactors. The performance of the electrochemical reactor correlates strongly to mathematical equations derided from the fluid hydrodynamic theory. The standard deviation (S.D.) of the measured and calculated performance is 2.8%. These results suggest that equations derived in conventional reactor technology are applicable in microsystems.