This study investigates the issues involved in the design of compact two-phase thermosyphon systems. In such systems the locations of the evaporator and condenser need be given a high degree of freedom. Anticipating situations where gravity does not provide sufficient potential to drive the condensate, a pump-assisted circulation loop was studied. Also, enhancement of boiling heat transfer in compact space was achieved by at enhancement structure having mutually connected microchannels. The key components used in the experiment are; a simulated chip (0.907 cm2) with an enhancement structure (6.8 mm high), a dielectric coolant (PF-5060, boiling point 56 °C), a naturally cooled condenser occupying a 6.5 × 6.5 × 17.8 cm3 volume, and a displacement pump (2 − 40 ml/min). The relative height between the evaporator and the condenser, the pumping rate, and the heat input were systematically varied. Theseparameters affect the overall thermal resistance from the chip to the ambient in a complex way. However, close examination of the data suggests that there could be an optimum point in the parametric domain where the thermal resistance is minimized with a least assistance from the pump.