Gender disparities in science, engineering, technology, and mathematics (STEM) degrees continue to be a global problem. Increasing equitable participation in STEM majors requires understanding how and why these disparities arise. This study examined relationships between female's selection of a STEM major, personality, STEM interest, STEM self-efficacy, and mathematics anxiety, and the relationship between those factors that affects gender disparities. Quantitative survey data from established instruments on these factors were collected from 128 female undergraduate students, including STEM (n = 60) and non-STEM majors (n = 68). Multiple Linear Regression, Binary Logistic Regression, and MANOVA were used to determine STEM self-efficacy. STEM self-efficacy was a significant variable explaining STEM interest, math anxiety, and majoring in STEM. The personality trait of openness was more significant in the female STEM majors than the non-STEM majors. This research has implications for identifying female STEM majors who may have math anxiety, decreasing those students' math anxiety, and recruiting females who would be open to a STEM career.