Background: This study was designed to determine the effect of perceived supports and barriers on self-efficacy beliefs and other social-cognitive variables related to second-year science, technology, engineering, and mathematics (STEM) students' career development. Social cognitive career theory (SCCT) states that career interest is influenced by four cognitive-person variables: self-efficacy beliefs, outcome expectations, interests, and goals. Other variables, such as social supports and barriers, also play an important role. Purpose: This study explores the influence of gender and STEM major on perceived supports and barriers. It also analyzes the effects of perceived supports and barriers on the SCCT cognitive-person variables. Method: Participants were 811 sophomore students in STEM programs at the University of Oviedo, Asturias, Spain. Kruskal-Wallis and Mann-Whitney U tests analyzed the difference in the perceived supports and barriers by gender and students' major. Multiple-group structural equation modeling was implemented to predict the relationship between perceived supports and barriers and SCCT cognitive-person variables. Results: The engineering students perceived more teaching staff barriers and fewer teaching staff supports than other students. Male software and hardware engineering students perceived more barriers than other male engineering students. The fit of the model revealed an important effect of perceived teaching staff supports on the four cognitive-person variables. Conclusions: To determine the influences on the cognitive-person variables, it is necessary to analyze the perceived supports and barriers. Peers and family are the most important perceived supports, while teaching staff and financial difficulties are the greatest perceived barriers.