The analytical determination of the spreading resistant as appears in electronic cooling applications is the subject of the investigation. A selected system consists of solid blocks of different sizes attached to each other; mainly to accelerate cooling effect by spreading the induced heat from a die structure. The objective is to provide a steady state analytical solution for a system that consists of two rectangular bodies of different size attached to each other. Then, using the function specification technique, the heat flux at the interface is analytically determined. The convergence of the analytically acquired data becomes an important issue and the related information is presented. It was remarkable this analytical solution technique is equivalent to a standard inverse methodology. (C) 2012 Elsevier Ltd. All rights reserved.