The aim of this study was to investigate how to develop prospective chemistry teachers' TPACK and thus qualify them for the effective use of educational technology in their future chemistry teaching. For this purpose, we developed and evaluated a university seminar for the professional development of preservice chemistry teachers. We implemented this seminar at two German universities with students of two different expertise levels and courses of study. One group of students consisted of master students with an imminent internship semester while the other comprised bachelor students. In order to find out how preservice teacher training for digital literacy should be structured we measured the participants' development considering their TPACK competence in lesson planning, TPACK self-efficacy, and attitude. The results revealed that the seminar is suitable for increasing the participants' TPACK since we were able to improve the students' skills to implement educational technology into their lesson plan. Yet, the residual comparison between both groups shows a significantly higher increase in the master students' abilities. Regarding the TPACK self-efficacy and attitude, however, we were able to measure a significant increase for only the master students. Based on our findings, we suggest to allocate a seminar on educational technology in direct link to an internship and at a time during their studies when the teacher candidates have already had the opportunity to gain some prior knowledge in content, pedagogy, and subject didactics.