A method of removing a photoresist may include permeating supercritical carbon dioxide into the photoresist on a substrate having a conductive structure including a metal. The photoresist permeating the supercritical carbon dioxide may be easily removable. The photoresist permeating the supercritical carbon dioxide may be removed using a photoresist cleaning solution from the substrate. The photoresist cleaning solution may include an alkanolamine solution of about 8 percent by weight to about 20 percent by weight, a polar organic solution of about 25 percent by weight to about 40 percent by weight, a reducing agent of about 0.5 percent by weight to about 3 percent by weight with the remainder being water. The photoresist may be easily removed without damaging the conductive structure in a plasma process.