As cooling requirements for electronic devices, e.g. computer processor units, power modules, etc. increase beyond the capabilities of air-cooling, interest has moved to several alternatives such as thermoelectric coolers, impinging jets and heat exchangers with phase change. Included among these, the capillary pumped loop is a very competitive cooling device, because of its performance reliability, no power requirements and low manufacturing cost. In this paper, a heat spreader employing capillary pumped loop principles was made of aluminum and copper and tested. The copper CPL heat spreader with heat sinks and fans on the condenser (86mm thick, 60mm wide, 181mm long) has demonstrated a cooling capacity of 640W at atmospheric pressure in the vertical orientation and maintains a difference between TIHE (temperature of the interface between heater and evaporator) and TAMB (ambient temperature) lower than 100°C.