This article gives an experimental evidence of the working principle of thermal semiconductor (TSC) devices proposed by dos Santos Bernardes (2009) [1]. For that, TSC working principle is introduced and the experimental procedures adopted for thermal conductivity measurements of a prototype are described. The prototype positioned appropriately between hot and cold plates of the test apparatus revealed heat flux asymmetry with reverse positioning, achieving a diodicity of 0.068 +/- 0.0025. The disclosure of this behavior supports experimentally the functionality of the TSC mechanism as a thermal diode. (C) 2014 Elsevier Ltd. All rights reserved.