A method for designing microreactors for isothermal operation with multiple highly exothermic or endothermic reactions under the conditions of fluid flow in a laminar flow state between two parallel plates is discussed. The formulated design procedure is based on a correlation between the fluid conditions and the heat properties; the operational conditions required for, e.g., a desired heat removal rate can be observed using the provided contour charts. The applicability of the proposed design method was verified using computational fluid dynamics simulations. In addition, the superiority of the microreactors is discussed specifically on the basis of the knowledge from the created charts. A method is proposed for designing microreactors for isothermal operation with highly exothermic or endothermic reactions. The proposed design method is based on the relationship between the fluid conditions and the heat properties. The contour charts produced describe the required operational conditions, which were validated via computational fluid dynamics simulations.