Fluid °ow and heat transfer in the entrance region of rectangular microchannels of various aspect ratios are numerically investigated in the slip-°ow regime with particular attention to thermal creep e®ects. Uniform inlet velocity and temperature pro¯les are prescribed in microchannels with constant wall temperature. An adiabatic section is also employed at the inlet of the channel in order to prevent unrealistically large axial temperature gradients due to the prescribed uniform inlet temperature as well as upstream di®usion associated with low Reynolds number °ows. A control-volume technique is used to solve the Navier
Stokes and energy equations which are accompanied with appropriate velocity slip and temperature jump boundary conditions at the walls. Despite the constant wall temperature, axial and peripheral temperature gradients form in the gas layer adjacent to the wall due to temperature jump. The simultaneous e®ects of velocity slip, temperature jump and thermal creep on the °ow and thermal patterns along with the key °ow parameters are examined in detail for a wide range of cross-sectional aspect ratios, and Knudsen and Reynolds numbers. Present results indicate that thermal creep e®ects in°uence t

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