This work presents measurements of the friction and heat transfer coefficients in 2D minichannels of 1.12 mm to 300 pm in thickness. The friction factor is estimated from the measured pressure drop along the whole channel. The heat transfer coefficient is determined from a local and direct measurement of both temperature and heat flux at the wall using a specific transducer. The experimental results are in good agreement with classical correlations relative to channels of conventional size. The observed deviations are explained either by macroscopic effects (mainly entry and viscous dissipation effects) or by imperfections of the experimental apparatus. (c) 2005 Elsevier Ltd. All rights reserved.