The recently reported 2D successive network reduction (SUNRED) algorithm has been extended to solve thermal or electro-static fields in 3D. The paper presented the models and the solution algorithm of the 3D version and discusses in details the efficiency of the new 3D-field solver. Comparisons with other solvers demonstrate the superior features of SUNRED. The tool extensively supports the compact thermal model generation of the analyzed structure. A novel type of analysis, the time constant analysis is introduced in the paper.