An apparatus for a reactive treatment of the surface of a workpiece, in which a process gas is brought into a chamber and a direct voltage arc discharge is generated in the chamber, the arc discharge is assisted or maintained, respectively by introducing a flow of charged particles. In known treatment methods, plasma generated in the direct voltage arc are generally distributed non-homogeneously in the inner space of the chamber and the area with a density of the plasma which is sufficient for the reactive surface treatment is relatively small. According to the invention this problem is solved in that the distribution of the effect of the treatment of the plasma in the chamber at least along a predetermined plane is set, and specifically by a distribution of openings for the process gas over a given area and/or by a distribution of the arc discharges in the chamber over a given area. The flow of charged particles enters into the chamber via a plurality of distribution openings. By such an arrangement, spatially large plasmas having high densities of ionization and acceptable densities of energy are realized, and it is possible to perform treatment of large surface areas and also treatment processes on objects which are thermally sensitive.