The quad flat non-lead (QFN) package is a both chip scale package and plastic encapsulated package with a copper leadframe substrate. The purpose of this paper was to establish the wideband equivalent circuit model of QFN packages for RF applications. Only short-path configuration was required for S-parameter measurement to achieve this purpose. Comparison of S-11 and S-21 between S-parameter measurement and optimized equivalent circuit model verified that those results were well matched and optimized. The parasitic parameters of the equivalent circuit were reliable up to 6 GHz. The methods proposed in this paper reduce the costs for samples preparation and chip simulation run time. In order to realize the package performance for higher frequency applications further, a 3D structure electromagnetic field simulator, HFSS, was used to simulate from 0.1 to 20 GHz for five modified package structures. Simulation results indicated that the QFN32 package that utilized the double bonding wires with a lower dielectric-constant molding compound and larger die-pad is the best structure for RF applications. (C) 2002 Elsevier Science Ltd. All rights reserved.