A semi-empirical analytical method called as the equivalent junction transformation has been proposed in this paper for the first time, and used to predict the breakdown characteristics of curved-abrupt P-N junctions. Based on this method, the effects of the radius of curvature of the metallurgical junction and the background doping concentration on the breakdown voltage, peak electrical field and depletion layer width at breakdown for cylindrical- and spherical-abrupt junctions are discussed in detail. All analytical results have shown in excellent agreement with the numerical analysis, showing the validity of the method presented here.