In one general aspect, an apparatus includes a metal or metal silicide contact layer disposed on an n-well region of a semiconductor substrate to form a primary Schottky diode. The apparatus includes a p-well guard ring region of the semiconductor substrate abutting the primary Schottky diode. The metal silicide contact layer has a perimeter portion extending over the p-well guard ring region of the semiconductor substrate and the p-well guard ring region has a doping level establishing a work function difference relative to the perimeter portion of the metal silicide contact layer to form a guard ring Schottky diode. The guard ring Schottky diode is in series with a p-n junction interface of the p-well region and the n-well region and the guard ring Schottky diode has a polarity opposite to that of the primary Schottky diode.