The thermal behavior of a square nickel plate micro-cooler holding 128 micro-channels in radial arrangement has been investigated. The device is to be used in microelectronic packaging cooling applications. In our study it was attached to a power transistor which was used as a dissipator and a temperature sensor. The thermal transient response to a dissipation step of the transistor was recorded in the measurement. The measured transients (cooling curves) were transformed into structure functions from which the partial thermal resistance corresponding to the cooling assembly was identified. The measurement and the partial thermal resistance identification was carried out at different flow-rates of nitrogen gas forced through the micro-channels. This way thermal resistance vs. flow-rate and heat-transfer coefficient vs. flow-rate characteristics of the investigated micro-channel cooler were derived. © 2005 IEEE.