In our research work it's considered Due to the high performance of electronics components, Heat Dissipation becomes a significant issue for stable operation of components. Micro channels provide very high heat transfer coefficients because of their small diameters. In this study, two dimensional fluid flow and heat transfer in a rectangular micro channel heat sink are analysed using FLUENT as solver with water as cooling fluid. With strong literature study it is found that down to 50 μm of hydraulic diameter, macro scale model can be applicable. Three channels of height 50 μm, 100 μm and 150 me are considered. The study is mainly focused on Nussle Number and height effects on micro channel thermal performance. The highest temperature is encountered at the heated surface of the heat sink immediately above the channel outlet.