Highly subcooled flow boiling at high heat flux in a rectangular minichannel of 2 mm × 2 mm in dimension was experimentally investigated. The channel was heated only from the bottom wall of the channel and it is regarded as a model of cooling components on electric devices in mobile gears. Under the condition of high subcooling and high heat flux in the stagnant pool and conventional scale channel flow, many fine vapor bubbles are emitted from primary vapor bubbles on heated surfaces. This boiling regime is called microbubble emission boiling (MEB). If we realize MEB in a minichannel, high heat flux due to vaporization will be obtained and large pressure loss due to confinement of bubble will be avoided. This paper first reports the results of our early experimental investigations on MEB in a pool boiling system to introduce the appearance of MEB. In flow boiling experiment, we reborts heat transfer characteristics and photographic observation.