Prior research has demonstrated that women and racial minority undergraduate students experience stereotype threat in unwelcoming STEM classrooms in predominantly White institutions. Drawing from focus group and journal entry data with Latinx and African American undergraduate students (N = 52) majoring in a STEM field at an institution that holds both Hispanic Serving Institution (HSI) and AANAPISI designations in Southern California, we find that Latinx and Black undergraduate students narrate exclusion from faculty and peers in four main ways: (1) exclusionary STEM classroom culture fomented by faculty, (2) study group stereotype threat, (3) nuances in Black student undergraduate experiences, and (4) unaddressed gendered discrimination. We find that Latinx and African American undergraduates enrolled at a minority serving institution highlight that STEM faculty foment stereotype threat in their classroom culture, which trickles down to students and negatively impacts their ability to develop the necessary social capital networks with both faculty and peers to succeed.