A method of fabricating an interposer includes: providing a carrier substrate; forming a unit redistribution layer on the carrier substrate, the unit redistribution layer including a conductive via plug and a conductive redistribution line; and removing the carrier substrate from the unit redistribution layer. The formation of the unit redistribution layer includes: forming a first photosensitive pattern layer including a first via hole pattern; forming a second photosensitive pattern layer including a second via hole pattern and a redistribution pattern on the first photosensitive pattern layer; at least partially filling insides of the first via hole pattern, the second via hole pattern, and the redistribution pattern with a conductive material; and performing planarization to make a top surface of the unit redistribution layer flat. According to the method, no undercut occurs under a conductive structure and there are no bubbles between adjacent conductive structures, thus device reliability is enhanced and pattern accuracy is realized.