In this paper we present thermal analysis of three kinds of ceramic package designs for high power LEDs. The analysis was made by transient thermal measurement and thermal simulation using the Finite Volume Method. The three ceramic packages under investigation employ same configuration of GaN-based chip, but they have different size and distribution of thermal vias. Three designs of LED packages resulted in significantly different thermal behaviors. Thermal behaviors, described as thermal resistance, of the three packaging designs were compared and evaluated as functions of bulk thermal resistance, spreading resistance, and surface roughness. The deviation between the simulated results and measured data were attributed to the different surface roughness in the interfaces between the packaging components. It was demonstrated that the junction temperature decreases with the effective contact area ratio in the LED packages. (C) 2006 Elsevier B.V. All rights reserved.