Here we present an investigation of boiling incipience in parallel micro-channels and compare the results with those reported for conventional channels. To provide additional insights into the role of surface roughness on the onset of nucleate boiling (ONB) in micro-channels, the roughness parameters were studied extensively. Onset of nucleate boiling is investigated in uniformly heated parallel rectangular micro-channels of D-h = 297 mu m with subcooled water flow at mass flux of 15.4-77.1 kg/m(2)s. It is shown that in the literature significant disagreement between values of wall temperature and the average mass liquid temperature at ONB point is due to different experimental conditions. For the analysis of the conditions at which the ONB occurred, the parameter based on the relation of the difference between wall excess temperature and bulk fluid temperature at ONB to the difference between saturation temperature and fluid inlet temperature is developed. The experimental results indicate that parameters, which affect incipience of nucleation in micro-channels, such as cavity radius and wall excess temperature, are well predicted by the theoretical nucleation criteria, which were developed for conventional size channels. (C) 2012 Elsevier Ltd. All rights reserved.