In 2000 several STEM faculty at Bethel College in Kansas designed and began offering a one-week intensive residential summer research experience for high school students--the Bethel College Summer Science Institute. The core idea underlying the design was to motivate students through the excitement of discovery. This event has been offered annually since that time and emphasizes collaboration with others during the research process, learning laboratory techniques, systematic data recording, data analysis methods, formal oral presentation of research results, exposure to cutting-edge STEM topics, and a residential experience with recreational activities mentored by college STEM students. Research topics have varied across STEM disciplines, including biology, psychology, chemistry, neuroscience, computer science, engineering, mathematics, and astronomy. Instruction involves a bare minimum of didactic presentation with emphasis on active involvement in laboratory or field activities. Instructional groups of 12 or fewer students, taught by 1 or 2 faculty with 1 or 2 undergraduate assistants, are further divided into groups of 2 to 4 students for individual projects, of which the results are presented in an afternoon symposium at the conclusion of the institute. The institute was funded primarily with student fees for the first decade of its existence, though enrollment, especially of underserved students, appeared to be limited by the $325 fee. In 2009 STEM alumni of the College were offered the opportunity to support individual students through donations, and fees were set at $50 in 2010. Enrollment tripled in 2010 and has remained at this level to the present; alumni donations have been adequate to cover expenses. Many students report that this support was crucial to their attendance and that the experience increased their desire to pursue study and careers in STEM fields (mean greater than 4 on a 1-to-5 scale for both attendance and desire). Approximately 17 % of Institute attendees have eventually matriculated to Bethel College, greatly enhancing the financial sustainability of the event. STEM alumni have responded very favorably to this opportunity for a significant impact on the development of young STEM students and on STEM enrollment at their alma mater. The approach described here can be replicated at other institutions as a strategy to build STEM enrollments and to engage STEM alumni in this effort.