Thermal control of electronic components is a continuously emerging problem as power loads keep increasing. To solve these thermal problems impinging jets are generally used in engineering, science and industry for its good heat transfer performance. In this study; cooling of a flat plate under constant heat flux condition, inside a rectangular channel, consisting of one open and three blocked sides was experimentally and numerically investigated using a single air jet flow. The impingement surface was a copper plate of the same width as the jet nozzle. Inlet flow velocities were measured using a Laser Doppler Anemometer (LDA) system. Temperature measurements were performed using thermocouples. Local and mean Nu numbers were determined as a function of two parameters, (a) Jet-to-plate distance (H/D (h)) in the range of 4-10 and (b) Reynolds number based on the hydraulic diameter of the slot nozzle in the range of 4000-10,000 (corresponding to an exit jet velocity from 6.5 to 16.2 m/s). Numerical investigation was also performed. Low Re number k-epsilon turbulence model was used during investigations. The results are presented in the form of graphs showing the variation of the local Nusselt number as a function of these parameters. The effect of Re number on local Nu number was examined for qaEuro(3) = 1000 W/m(2) and H/D (h) = 6. In general, it was observed that heat transfer is sensitive to the Reynolds number and increases with increasing Re number. Average Nusselt number increases of 49.5 % from Re = 4000 to Re = 10000. Effect of H/D (h) on heat transfer under impinging air jets was examined with local Nusselt numbers. Local Nusselt number was less sensitive to H/D (h) in the range of H/D (h) = 4-10. Average Nusselt number decreases of 17.9 % from H/D (h) = 4 to H/D (h) = 10. The highest average Nu number was achieved for Re = 10,000 and H/D (h) = 4. The numerical results agreed well with the experimental data, including local and average Nusselt numbers. Correlations are proposed to predict the local Nusselt number as a function of Re number and H/D (h.).