Abstract The hexagonal pattern of the voltage-sustaining layer in the COOLMOST with p-region in the center of each unit cell, which produces the lowest specific on-resistance, is studied based on a technologically achievable minimum aspect ratio of the width of each region to the thickness of the voltage-sustaining layer. A breakdown voltage higher than the previous result is also achieved by breaking the requirement of the different peak fields to be equal. Furthermore, the doping of the p-region near the drain is modified to get a better result. It is believed that this is the new theoretical “Silicon Limit”. The results show that a value of R on less than 1/3 of the previous one is obtained. Theoretical analysis is given and shows in good agreement with the numerical simulation.