The aim of this study is to learn how a series of 3-day international seminars, emphasizing networking, and an academic writing, reviewing, and leading discussions, supports PhD students' professional learning and development by providing both a formal and non-formal context. The sample of this study consisted of PhD students from three countries -- Estonia, Finland and Israel, and study was carried out in 2022 (in-person seminar; n = 20) and 2023 (hybrid seminar; n = 17). After the carefully designed 3-day seminars (including plenary lectures, workshops, and non-formal reflection sessions for PhD students), the feedback was asked from all participants in a format of questionnaire. In addition, interviews with two PhD students from each country were carried out to validate the outcomes from the questionnaire. Based on the results, non-formal activities were seen as supportive for getting to know their fellow PhD students and experienced academics in the field of science education. For many students, presenting their work or undertaking a review for another PhD student was a first-time experience and therefore gave them the opportunity to experience a wide range of activities supportive of being a researcher. In future studies, supporting PhD students long-lasting motivation to work on a doctoral thesis and to commit to PhD studies, can be used as one of the design principles in these types of seminars.