This paper evaluates and compares the effects of conventional and unconventional monetary policies on the corporate debt structure in the United States. It does so by using a vector autoregression in which policy shocks are identified through high‐frequency external instruments. Our results show that both monetary policies shift the firms’ composition of external financing, though in a different way. An expansionary conventional (unconventional) monetary policy leads to a rise (decline) in loans and a decline (rise) in debt securities issuance. Our results suggest that unconventional monetary policy operated primarily through a portfolio rebalancing channel, rather than through a bank lending channel.