This paper describes the development of radial grooved micro heat pipes (MHPs) with a three-layer structure. The MHPs were designed to allow separation of the liquid and vapor flow to reduce the viscous shear force. The 5×5 cm2 MHP array was fabricated by using bulk micromachining and eutectic bonding techniques on 4-in. (1 0 0) silicon wafers. Experiments were undertaken to evaluate the performance of wafers with three different wafer fill rates at different input powers. We glued a heater below the evaporator section, pumped cold water through a square copper heat exchanger above the heat pipe, and pasted 15 K-type thermocouples on both sides of MHP structure to record the variations of surface temperature. After the evaluation, the MHP with 70% fill rate showed the best performance as compared to samples with smaller fill rates.