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The fluid-dynamic and heat transfer experimental analysis of a gas turbine internal three-pass blade cooling channel is presented. The passage is composed of three rectilinear channels joined by two sharp 180 degree turns; moreover, the channel section is trapezoidal instead of rectangular configuration, already analysed in depth in the literature. The trapezoidal section is more representative of the actual geometrical configuration of the blade and, in comparison with the rectangular section, it shows significant aspect ratio and hydraulic diameter variations along the channel. These variations have a strong impact on the flow field and the heat transfer coefficient distributions. The flow analysis experimental results - wall pressure distributions, flow visualisations - are presented and discussed. The heat transfer coefficient distributions, Nusselt enhancement factor, obtained using thermocromic liquid crystals (TLC), have been studied as well. In order to understand the influence of the cooling mass flow rate, a wide range of flow regimes - Reynolds numbers - has been considered. [ABSTRACT FROM AUTHOR]