A metal/insulator/metal capacitor and a fabrication method thereof are presented. The method includes forming a first electrode on an insulation film; forming a side wall made of insulating material on a side surface of the first electrode; forming an interlayer insulation film on the top surface of the insulation film including the first electrode and the side wall; forming a via hole to expose the first electrode by selectively etching the interlayer insulation film such that an edge area at which a side surface and a bottom of the via hole intersect is positioned on a top surface of the side wall; forming a dielectric layer on an inner wall of the via hole; forming a second electrode on the dielectric layer such that the via hole is filled; and forming a metal wire on the second electrode such that the metal wire is electrically connected to the second electrode.