It is critical to adopt an intersectional approach integrating gender and ethnicity in university-level studies of STEM (science, technology, engineering, and mathematics). This perspective is vital for recognizing the variety of existing viewpoints and addressing the underrepresentation of Indigenous peoples, especially Indigenous women in STEM fields. These groups face triple discrimination based on ethnicity, gender, and economic status throughout all levels of education. A qualitative methodology is employed to address this issue, focusing on the theoretical validation of the Questionnaire on the Intersectionality of gender and ethnicity in Higher Education in STEM (QISHESTEM) through expert judgment. This validation considers the criteria of clarity, coherence, relevance, and sufficiency to ensure the quality and pertinence of the instrument in the Mexican context. The aim is to ensure that the instrument effectively captures university students’ opinions on how ethnic origin influences their choice of STEM careers. The validation confirms that QISHESTEM is a reliable tool for this purpose, highlighting its role in identifying specific barriers and promoting equity in STEM education in Mexico.