A microfluidic device comprises at least one reactant passage defined by walls and comprising at least one parallel multiple flow path configuration comprising a group of elementary design patterns being able to provide mixing and/or residence time which are arranged in series with fluid communication so as to constitute flow paths, and in parallel so as to constitute a multiple flow path elementary design pattern, wherein the parallel multiple flow path configuration comprises at least two communicating zones between elementary design patterns of two adjacent parallel flow paths, said communicating zones being in the same plane as that defined by said elementary design patterns between which said communicating zone is placed and allowing passage of fluid in order to minimize mass flow rate difference between adjacent parallel flow paths which have the same flow direction.