The purpose of this study was to answer the following two questions: (1) Do significant differences exist in high-school learning experience, interests, self-efficacy, and career aspirations between male and female science, technology, engineering, and mathematics (STEM) students? (2) Can high-school learning experiences, interests, and self-efficacy significantly predict career aspirations, and do differences exist between male and female STEM students? This study highlighted the gender gap between male and female university students who had already chosen STEM majors with similar academic ability. A total of 407 first-year students were surveyed at a 4-year research university in Taiwan. For the data analysis, a t-test and multiple regression analysis were used, and the findings indicated that male STEM students had greater family support than their female counterparts. The variable of task value could significantly predict STEM career aspirations for both male and female students, whereas the variable of STEM course self-efficacy could only significantly predict that of male students. In conclusion, the findings highlighted that the motivation of task value was a vital factor for predicting STEM career aspirations, whereas the factor of family support was the main gap between male and female STEM students in terms of their high-school learning experiences.