Jet impingement cooling is an effective way for thermal management in electronics, prevailed over many other single heat transfer modes. In general, jet arrays are better than a single jet, enhancing jet cooling performance. However, the performance of jet arrays is strongly dependent on the jet configurations, e.g., adjacent jet interval and hole-to-surface distance. Thus, in this study, jet impingement cooling is investigated on a flat heating surface placed in a channel, including in-line double jet cooling, in-line three jet cooling, and in-line four jet cooling. It is known that the outlet configuration could influence the jet performance because of the crossflow effect, and herein the outlet is designed to have intermediate crossflow only. The local Nusselt number distribution is experimentally measured by the liquid crystal method. Then the effect of the adjacent jet interval on the jet cooling performance on the target surface is compared. It is found that the jet array indeed enhances heat transfer. For example, based on the results, it is seen that in comparison to crossflow cooling, the average Nusselt number is improved by 34% by the in-line double jet cooling, and correspondingly the maximum Nusselt number is enhanced by 51%.