The manifold microchannel is expected to be an efficient heat dissipation solution for electronic devices. In this chapter, microcolumn structures are added to the manifold microchannel to enhance heat transfer. The effects of column-array arrangements, column shapes, and offsets on heat transfer and flow are numerically investigated. The flow and heat transfer characteristics of the rhombic single-row staggered arrangement in subcooled flow boiling are numerically studied. The results show that the single-row staggered arrangement has the best overall performance among the four column-array arrangements. At the same pumping power, the thermal resistance of the rhombus is at most 14.9% smaller than that of the circle, which indicates the best overall performance. The thermal resistance of the optimized MMC is smaller than that of the traditional one at the same pumping power. The thermal resistance for the single-row staggered arrangement is the lowest and decreased by 43.3%–46.7% compared to the traditional one. In subcooled flow boiling, the average temperature of the heated surface has stabilized with very small fluctuations. The fluctuation range of pressure drop is 2 kPa and the maximum fluctuation rate is only 9.3%. This suggests that microcolumns are able to reduce boiling instability. The reason for the fluctuation of pressure drop is the large bubbles near the outlet whose volume changes with time.