A method of producing an epitaxial wafer, comprising: performing epitaxial growth of silicon on a main surface of a wafer made of a silicon single crystal; performing surface flattening pretreatment of a main surface of the wafer using a treatment liquid of a predetermined composition at a temperature of 100.degree. C. or less, thereby forming an oxide film of a predetermined thickness while removing particles adhered on the main surface of the wafer; and performing a surface polishing step where the main surface of the wafer is mirror polished.