Having a sense of belonging can promote persistence in the STEM fields, but less is known about what it means to develop that sense of belonging. To investigate this phenomenon, we conducted semi-structured interviews with a cohort of STEM students (n = 10) nearing graduation at an urban university regarding their sense of belonging and qualitatively coded the interviews using thematic analysis. Results revealed that all interviewed students clearly articulated feelings of belonging, making them an ideal population from which to learn more. We applied two frameworks to guide our understanding of what factors promoted the development of a sense of belonging for these students: the Network Theory of Social Capital and the Counterspaces Framework. The students described their experiences in relation to elements of social capital and counterspace processes as they reflected on the development of feelings of belonging. One element of social capital, "reinforcement," or assurance and recognition of one's worthiness as a member of a group, was the most prevalent element of social capital influencing the participants' development of a sense of belonging. "Direct relational transactions," or the exchange of resources within a community, was the most prevalent counterspace process discussed by the participants. Our findings expand the utility and add to the theoretical underpinnings of the two frameworks, indicating that gaining social capital and experiencing counterspaces can contribute to undergraduate STEM student development of a sense of belonging.