Microreactors generally consist of microstructured plates containing a large number of equal channels. The small diameter of the channels enables high heat and mass transfer rates. To exploit this feature and realize a high throughput within a small volume, it is necessary to use high flow rates. However, at these high flow rates it is not straightforward to obtain an even distribution of fluid flow over the individual microchannels. A three-dimensional computational fluid dynamics (CFD) model was used to calculate the flow distribution on a microstructured plate. Calculation time was reduced by introducing an artificial viscosity in the channel region. The calculations show that a transitional velocity exists, below which the flow distribution is independent of velocity and above which inertia effects start to influence the distribution. To optimize the flow distribution, nine different plate geometries were studied at flow rates between 0. 1 and 100 in s(-1), or 4 x 10(-4) to 0.4 m(3) h(-1) per plate. By optimizing the plate geometry, the relative standard deviation of the flow distribution was reduced from 19 to 3%. Furthermore, it is shown that the optimal geometry depends on the flow rate, which thus needs to be taken into account in the design of microchannel plates.