The Berlin Mathematical School is the graduate school of the Cluster of Excellence MATH+ and a joint endeavor of the mathematics’ departments at the universities in Berlin: Freie Universität (FU), Humboldt-Universität (HU) and Technische Universität (TU).
For more information:
https://www.fu-berlin.de/sites/china/aktuelles/news/CfA_-PhD_-Berlin-Mathematical-School.html
http://www.math-berlin.de/images/guidelines/BMS_PhD_Application_Guidelines.pdf
You can apply at: http://www.math-berlin.de/application (Application with a bachelor’s degree are also possible.)