Owing to the increasing miniaturization and number of high-power-dissipating components in electronic packages, proper thermal management has become of vital importance. Numerical simulations were carried for three block-type elements representing electronic components located on the bottom plate of a rectangular channel. The top plate of the channel was parametrically examined in order to assess the radiative heat-transfer component. The effects of the air flow rate in the channel and the spacing, geometry, and emissivity of the blocks were investigated. Two types of heat sources were considered: A uniform heat-generation rate in each block and a point heat-source at the center of each block. Reynolds numbers varying from 10 to 1000 and block length-to-spacing ratio varying from 1 to 3.7 were considered in this work. The results clearly indicate that, when the radiative heat-transfer component is neglected, 33% of the heat generated is conducted through the bottom substrate while the remaining 67% is convected to the cooling medium. However, when the radiative heat transfer is considered in the analysis, the radiant heat loss is estimated to range from 4 to 8%, at a Reynolds number of 500.