Limited literature has investigated the effects of state and institutional merit-based financial aid on student choice of science, technology, engineering, and mathematics (STEM) major fields, an unintended consequence with important implications. By leveraging nationally representative longitudinal data from the Beginning Postsecondary Students, we examined these effects--respectively and jointly--with logistic regressions (LR) and propensity score matching (PSM). Both the LR and PSM results showed that students who receive both state- and institution-awarded merit aid were more likely to major in STEM. For students who only received state-awarded merit aid, the PSM presented significant and positive effects while the LR did not. Institution-only merit aid had no statistically measurable effect. We discuss implications for research, policy, and practice for state- and institution-based financial aid.