Background: Closing the gender gap in science, technology, engineering, and mathematics (STEM) disciplines is essential for achieving social equity and advancing innovation and socioeconomic development, as outlined in the Agenda 2030 for Sustainable Development. Despite notable progress, persistent stereotypes continue to restrict women's aspirations and limit their access to traditionally male-dominated STEM careers, thereby influencing their social cognition and decision-making. This study examines implicit gender-career biases among STEM students by analyzing reaction times (RTs) from the implicit association test (IAT) while investigating how these biases vary across sexes and gender identities, with particular attention to their disproportionate impact on women. Results: A quantitative, cross-sectional experimental design was employed. The IAT was administered with blocks 3 and 4 representing stereotype-consistent tasks and blocks 6 and 7 representing stereotype-inconsistent tasks. In the sex-based analysis, participants classified as female exhibited significant differences between blocks 3 vs. 6 (p < 0.001) and blocks 4 vs. 7 (p < 0.001), whereas those classified as male showed a significant difference only between blocks 4 vs. 7 (p < 0.001). In the gender-based analysis, respondents who self-identified as women demonstrated significant differences between blocks 3 vs. 6 (p = 0.001) and blocks 4 vs. 7 (p < 0.001), while participants who self-identified as men exhibited a significant difference only for blocks 4 vs. 7 (p < 0.001). Non-binary participants showed significant differences for both comparisons, blocks 3 vs. 6 (p = 0.004) and blocks 4 vs. 7 (p = 0.049). In contrast, individuals reporting other gender identities exhibited a significant difference only between blocks 4 vs. 7 (p = 0.015). Conclusions: The findings reveal that implicit gender-career associations disproportionately affect both individuals classified as female and those identifying as women or non-binary, shaping their perceptions and attitudes toward STEM. This underscores the urgent need for targeted educational interventions to mitigate these biases and promote gender equity in higher education. Addressing these cognitive barriers can enable institutions to enhance the retention and success of underrepresented groups, ultimately harnessing the full potential of diverse talent in STEM.