A budesonide (BDS) suspension was obtained via advanced supercritical carbon dioxide (scCO2) processing. Thereafter, the suspension was freeze-dried (FD) to produce BDS particles for dry powder inhaler formulations (scCO2/FD processing). The scCO2/FD processed BDS powder showed low crystallinity by powder X-ray diffraction and a rough surface by scanning electron microscopy. The respirable fraction of BDS was assessed using a twin impinger and revealed that the amount of the scCO2/FD processed sample that reached stage 2 was 4-fold higher than that of the supplied powder. To extend the utility of scCO2 processing, BDS particles for dry powder inhalers were fabricated by combining the scCO2 system with various additives. When BDS was processed via scCO2/FD in the presence of the novel additive, namely, monoglyceride stearate (MGS), the residual BDS/MGS particles remaining in the capsule and devices decreased, followed by an increase in the respirable fraction of BDS 6-fold higher than with the supplied powder. The scCO2/FD processed BDS/MGS particles had a smooth surface, in contrast to the scCO2/FD processed BDS particles. A combination of BDS and an appropriate additive in scCO2 treatment may induce changes in particle surface morphology, leading to an improvement in the inhalation properties of BDS.