A micro-system consisting of micro-channels with integrated temperature sensors was successfully designed and fabricated for the study of heat-transfer properties of fluid flow in micro-domains. Surface micro-machining technology was used to construct the micro-channels with dimensions of about 40μm × 1.4μm × 4000μm. Polysilicon thermistors, 4μm × 4μm × 0.4μm in size were suspended across the channels and directly exposed to the fluid for local temperature measurements. The micro-channels and the micro-sensors were calibrated prior to the heat-transfer studies. Experimental results of temperature distributions along a micro-channel are presented. The integrated micro-system performance was analyzed to provide a framework for the interpretation of the experimental data, and the various heat-transfer mechanisms are subsequently discussed.