A new thin layer phantom for testing hyperthermia controllers has been constructed and evaluated using an ultrasound hyperthermia system. The phantom's thermal behaviour agrees with the characteristics of the Pennes' bio-heat transfer equation (BHTE). In particular, the experimental and theoretical results agree in the following ways. First, with respect to the power deposition: for a given power magnitude and scan radius, the shape of the temperature distribution across the phantom corresponds to the shape predicted by the BHTE and the experimental and theoretical temperature values agree closely; when the power magnitude is varied at a fixed scan radius, the average temperature of the phantom varies linearly with the applied power, and as the scan radius is varied at a fixed power magnitude, the average temperature increases with decreasing scan radius size. Secondly, with respect to perfusion: increasing or decreasing the flow rate over the phantom simulates an increase or decrease in the BHTE perfusion term, and the estimated perfusion values are dependent on flow rate only, and are not functions of power or geometry. The combination of these experimental and theoretical results validate the phantom's potential for testing feedback control systems, particularly for future use in the development and verification of model-based controllers. The use of this phantom should improve and accelerate the testing and evaluation of feedback control systems, and reduce the need for animal and human testing.