This qualitative descriptive case study explored the perceptions of high school STEM teachers surrounding the phenomenon of female high school STEM students not selecting a pathway into a STEM degree program in a post-secondary institution. Twenty-one STEM teachers completed the online questionnaire with semi-structured open-ended questions. From the questionnaire, perceptions were analyzed and used for a detailed discussion within a STEM focus group comprised of 12 participants. The transcripts from the questionnaire and focus group discussion were entered into NVivo 11 software for qualitative analysis. This study explored STEM teacher perceptions revealing hidden teacher bias that may explain the phenomenon of low female selection of a STEM pathway into a post-secondary STEM program. The analysis revealed themes that connected directly and indirectly to an overarching theme of culture. Connected to the theme of culture were sub-themes. The five sub-themes were: (a) hidden bias, (b) family, (c) socio-economics, (d) gender, and (e) self-concept. These emergent themes revealed where social cognitive theory impacts female decision-making through triadic reciprocal causation resulting in female student selection into or away from a STEM pathway after secondary education. Educational leaders using anti-bias professional development can counteract hidden bias in education and increase awareness of the effect teachers and leaders have on female STEM students.