This study presents findings on the physics identity development of female students in the German Physics Olympiad who participated in an intervention designed to support their engagement in physics. Enrichment programs such as the Physics Olympiad have been found to positively impact students' engagement and intent to pursue a career in science. However, many enrichment programs, including the Physics Olympiad, suffer from an underrepresentation of young women. The intervention investigated in this study capitalizes on gender-related research in physics education in order to explore ways in which gender equity can be raised in enrichment programs. To this end, we designed an identity-safe learning environment that facilitates participating young women's physics identity development. For example, same-sex groupings and considerately adopted physics contents that particularly acknowledge young women's interests (e.g., relation to medical issues and the human body) were utilized. Overall, 30 Olympians took part in a one-day intervention (13 females, 17 males). Positive effects in two important physics identity constructs, namely, interest and competence, for young women were found, while at the same time no effects were found for young men. Furthermore, the young women were more likely to participate in next year's Physics Olympiad, compared to the overall female Physics Olympiad population. These results indicate that the careful design of an intervention based on gender research and science identity theory can support young women's physics identity development.