A substrate processing apparatus includes a chamber configure to provide a space for processing a substrate, a substrate support configured to support the substrate in the chamber, an upper supply port provided in an upper portion of the chamber and configured to supply a supercritical fluid on an upper surface of the substrate, a recess provided in an upper wall of the chamber and having a diffuser shape whose diameter gradually increases from an outlet of the upper supply port, and a fluidic baffle disposed in the recess between the upper supply port and the substrate and including unit cells repeatedly arranged in a space with same phases and geometric sizes and in fluid communication with each other.