In this paper, thermal transient measurement has been used to study the thermal behavior of high power infrared (IR) emitter with different thermal interface materials. Furthermore, optical test has been carried out and optical power obtained through the optical test is used to correct the power dissipation for the computation of structure functions to obtain accurate values of real thermal resistance. In order to identify the point of separation between the package and metal-core-printed-circuit-board (MCPCB), dual interface method has been utilized by comparing the structure functions obtained by two thermal transient measurements with different thermal interface materials between the package and MCPCB. The real junction-to-case thermal resistance, Rth(jc) has been identified as point of separation of the structure functions. (c) 2012 Elsevier B.V. All rights reserved.