A micro-reflectron for a time-of-flight mass spectrometer including a substrate and integrated with the volume of the substrate, means for application of a potential gradient in a volume suitable for constituting a flight zone of the ions. The means of application includes at least two polarization electrodes and a wall of at least one resistive material that can be polarized between these electrodes so as to generate a continuous potential gradient, itself providing the function of reflectron, this flight zone, these electrodes and this wall being obtained by the technology of microelectromechanical systems (MEMS) and this micro-reflectron having a thickness of less than 5 millimeters while its other dimensions are less than 10 times this thickness.