Experiments are conducted for laminar forced convection of water in a microchannel under partially-heated and fully-heated conditions on one wall with negligible axial heat conduction. The microchannel had a trapezoidal cross-sectional shape, with a hydraulic diameter of 155 mu m and a heating length of 30 mm. Three-dimensional numerical simulations, based on the Navier-Stokes equations and energy equation, are obtained for forced convection of water in this microchannel under the same experimental conditions. It is found that the numerical predictions of wall temperatures and local Nusselt numbers are in good agreement with experimental data. This confirms that classical Navier-Stokes and energy equations are valid for the modeling of convection in a microchannel having a hydraulic diameter as small as 155 mu m. For a microchannel with the same cross-sectional shape with one-wall heated and a heating length of 100 mm, numerical results show that the thermal entrance length is given by z = 0.15RePrD(h), with the fully-developed Nusselt number approaching a constant value of 4.00. (C) 2008 Elsevier Ltd. All rights reserved.