The attachment of a shield to a heat sink enhances the thermal performance. But, forming slots in the shield increases thermal resistance. We found that increasing the slot width enhances the flow performance over the heat sink and this improvement continues as the number of slots increases, but the thermal performance, on the other hand, decreases. Slots work as a flow bypass and create jets to destroy eddies and vortices created by the shield. Therefore, pressure drop at Re = 55,000 for a slotted case is about 80% lower than a solid shield. For suitable thermal resistance and moderate pressure drop, the appropriate slotted shield will have 3–7 slots at different slot widths. These slots preserve the improvement of thermal resistance with a suitable pressure drop.