This paper presents thermal analyses of a poweramplifier placed in a wind tunnel. All the investigations arebased on the transient temperature measurements performedduring the circuit cooling process. The measured cooling curveswere used to compute the cumulative and differential structurefunctions for the circuit with a heat sink. These functions helpedto determine the optimal values of circuit model parametersnecessary for numerical thermal simulations. The experimentsdemonstrated the influence of the wind speed on the value of theheat transfer coefficient and consequently on the temperatureof the entire structure.