A method of fabricating a semiconductor may include forming on a substrate a mold structure including a mold layer, a buffer layer, and a support layer, performing on the mold structure an anisotropic etching process to form a plurality of through holes in the mold structure, and forming a plurality of bottom electrodes in the through holes. The buffer layer has a nitrogen content amount that increases as approaching the support layer from the mold layer. The buffer layer has an oxygen content amount that increases as approaching the mold layer from the support layer.