Many newly developed active pharmaceutical ingredients (APIs) are poorly soluble in water and thus have a dissolution-limited bioavailability. The bioavailability of Biopharmaceutical Classification System (BCS) class II APIs increases if they dissolve faster; this can be achieved by increasing their surface-to-volume ratio, for example, through formulation as submicron particles. In this paper, we develop a supersonic spray dryer that enables rapid synthesis of submicron-sized APIs at room temperature. Dispersing gas is accelerated to supersonic velocities in the divergent portion of a de Laval nozzle. The API solution is directly injected in the divergent portion and fully nebulized by impinging high velocity gas and pressure gradients across shocks at the exit of the nozzle. In such a device, we produce crystalline danazol particles with a Sauter mean diameter as small as 188 nm at a production rate up to 200 mg/h. The smallest particles with the narrowest size distributions are formed in overexpanded flows with a shock front close to the nozzle exit. Moreover, we demonstrate the scalability up to 1500 mg/h by increasing the danazol solution concentration; in this case, the Sauter mean diameter of the spray-dried particles increases to 772 nm.