Provided are a fin structure and a method of manufacturing a fin transistor adopting the fin structure. A plurality of mesa structures including sidewalls are formed on the substrate. A semiconductor layer is formed on the mesa structures. A capping layer is formed on the semiconductor layer. Thus, the semiconductor layer is protected by the capping layer and includes a portion which is to be formed as a fin structure. A portion of an upper portion of the capping layer is removed by planarizing, and thus a portion of the semiconductor layer on upper surfaces of the mesa structures is removed. As a result, fin structures are formed on sides of the mesa structures to be isolated from one another. Therefore, a fin structure having a very narrow width can be formed, and a thickness and a location of the fin structure can be easily controlled.