A method includes forming a dielectric layer over a conductive layer, and forming a sidewall spacer in an opening in the dielectric layer. The opening exposes a portion of the conductive layer. A bottom electrode layer is formed over the conductive layer and the sidewall spacer. A phase change material layer is formed over the bottom electrode layer, and a top electrode layer is formed over the phase change material layer. In an embodiment, the method includes recess etching the bottom electrode layer before forming the phase change material layer.