Language, and thus scientific language, is essential for chemistry teaching and learning. To be able to successfully teach the scientific language of chemistry, the Chemish, (prospective) chemistry teachers need to possess pedagogical scientific language knowledge (PSLK).Thus, teacher preparation needs to focus explicitly on Chemish and its teaching and learning. Therefore, this paper presents and discusses a case study on the development of a seminar unit to foster pre-service chemistry teachers' PSLK. In concrete, this includes (i) sensitizing pre-service chemistry teachers regarding Chemish, (ii) providing pre-service chemistry teachers with knowledge about Chemish and methods and tools to teach Chemish, and (iii) letting them develop their own teaching activities. The seminar unit's development follows the model of participatory action research in university teacher teaching. This paper presents the first cycle for piloting the seminar unit within an obligatory chemistry education course with eight pre-service chemistry teachers. The focus is put on the course of the seminar unit as well as the results of the first evaluation cycle using a mixed methods design. The evaluation reveals that pre-service chemistry teachers' pedagogical scientific language knowledge developed focusing on the three named components. In the meaning of a cyclical development, results are discussed and suggestions for further changes are made.