Liquid cooling in thermal management systems has been implemented mostly through the use of thermal interface materials, which introduce in in-series parasitic thermal resistances and reduced thermal performance. To achieve the full potential of liquid cooling, cooling structures should be fabricated directly in-chip, enabling effective heat transfer near the junction. In this work, we investigate an integrated cooling module encompassing enhanced fin structures (diamond-shaped and square pin fins) with an impinging jet manifold. Low thermal resistance of 0.1 cm2.K/W was achieved, while consuming a record low pumping power of 40μ W/mm2 using 25 μm channel width. Our approach was compared with bulky traditional fan cooling and no cooling cases, and resulted in 6.6x and 62 x reduction in thermal resistance, respectively. The cooling structure was directly fabricated at the back side of a GaN power IC which resulted in a thermal resistance of 1 K/W at 10 mW pumping power, 6.6 K/W thermal resistance was realized using fan cooling. Furthermore, 37 % increase in dynamic on-resistance (Ron) was reported at 10 W power dissipation using fan cooling, which was reduced to 12 % when using our approach at 15 W power dissipation.