The current study investigates how undergraduates reason about gender and racial inequity in fields related to science, technology, engineering, and math (STEM). Participants were 342 undergraduates from diverse ethnic backgrounds who answered an open-ended question about ethnic and gender disparities in STEM fields. Thematic analysis revealed substantial variation in how participants reasoned about these disparities. Corresponding quantitative analyses indicated that participants from various sociodemographic backgrounds tended to reason about STEM disparities in different ways. Women were more likely than men to mention stereotyping and lack of confidence as reasons for STEM inequity. Conversely, men were more likely than women to mention a lack of motivation as reasons for these disparities. Latinx participants were also more likely to mention stereotyping than participants from other ethnic backgrounds. Our results imply that there may be unique factors, like stereotyping and low confidence, that are of special concern to women and Latinx individuals when deciding whether or not to pursue STEM careers.