This work is aimed to study the effects of geometric design on the thermal performance of star-groove micro-heat pipes. A mathematical one-dimensional, steady-state model is developed from the first principles where the continuity, momentum, and energy equations of the liquid and vapor phases, together with the Young-Laplace equation, are solved numerically to yield the heat and fluid flow characteristics of the micro-heat pipe. The heat transport capacity and the corresponding optimal charge level of the working fluid are evaluated for different geometric designs and operating conditions. The unique geometrical design of the star-groove micro-heat pipes provides a better insight into the effects of various geometrical parameters, such as the cross-sectional shape, the acuteness of the corner apex angle, the number of corners, cross-sectional area and total length. Comparisons of the performance between the star-groove and regular polygonal micro-heat pipes are performed and the factors contributing to the enhancement of heat transport due to the variations of geometrical parameters are identified and discussed. (C) 2010 Elsevier Ltd. All rights reserved.