A vacuum pump system for evacuating a chamber, in particular a lock or a process chamber, is provided that includes a main vacuum pump preferably configured as a screw pump. An inlet of the main vacuum pump is connected with the chamber to be evacuated. As seen in the feeding direction of the main vacuum pump an auxiliary vacuum pump is arranged which is in particular a Roots pump. An outlet area of the main vacuum pump is connected with a main outlet on the one hand and an inlet of the auxiliary vacuum pump on the other hand. Further, an outlet of the auxiliary vacuum pump is connected with the main outlet.