Golub Capital BDC, Inc. is a business development company and operates as an externally managed closed-end non-diversified management investment company. It invests in debt and minority equity investments in middle-market companies that are, in most cases, sponsored by private equity investors. The company seeks to invest in the United States. It primarily invests in senior secured, one stop, unitranche, second lien, subordinated and mezzanine loans of middle-market companies, and warrants.