In this paper, a partition method is proposed to Study the high voltage devices with the step doping profile for the first time. It has been proposed that its breakdown voltage can be approached to that of the linearly graded devices with similar forward voltage drop (V-cc). In addition, by this method, the breakdown voltage can be deduced and its corresponding issue location is also fingered out in the step drift region. Furthermore. in order to reduce the undesirable additional masks, the degraded factor (D) is developed to obtain better performance with the least number of frames. Eventually, a 660 V step analytical results are compared with a 606.6 V MEDICI Simulation and this shows that the partition method is very effective. (C) 2003 Elsevier Ltd. All rights reserved.