A chip package includes a semiconductor substrate and a metal layer. The semiconductor substrate has an opening and a sidewall surrounding the opening, in which an upper portion of the sidewall is a concave surface. The semiconductor substrate is made of a material including silicon. The metal layer is located on the semiconductor substrate. The metal layer has plural through holes above the opening to define a MEMS (Microelectromechanical system) structure, in which the metal layer is made of a material including aluminum.