An apparatus and method for treating a substrate are provided. The apparatus includes at least one first process chamber configured to supply a developer onto the substrate; at least one second process chamber configured to treat the substrate using a supercritical fluid; a transfer chamber configured to transfer the substrate from the at least one first process chamber to the at least one second process chamber, while the developer supplied in the at least one first process chamber remains on the substrate; and a temperature and humidity control system configured to manage temperature and humidity of the transfer chamber by supplying a first gas of constant temperature and humidity into the transfer chamber.