I. Introduction
Increasingly demands of various semiconductor technologies e.g., GaAs HEMTs and InP HBTs, in terms of power, frequency, and applied high peak-to-average ratios broad band signals, have placed massive requirements on the accuracy of the device models used for design. New semiconductor material systems, e.g., GaN, have been developing at such a fast rate that conventional equivalent circuit modeling approaches may not be able to keep up.