In this paper

a simple theoretical formula for the distribution of electrical field and electrical potential of the planar n+ - p junction with floating field limiting ring-s（FFLR） is presented. This equation is deduced from the cylindrical symmetry solution of Poisson’s equation in combination with the boundary condition of the field limiting ring

with the assumption that the barrier of majority carriers formed around the rings is lower than leV and can be neglected. The theoretical design formula of the FFLR is also given. The conformity of theory with the result of experimental or mathematical analysis is satisfactory for practice.