A 3D transient investigation of the cooling of electronic chips inside a cavity and enhanced by a finned heat sink is studied numerically. Moreover, the impact of the position and number of electronic chips on their cooling, heat transfer, and fluid flow by natural convection-radiation inside the cavity is presented. Radiation exchange between enclosure walls is considered. Furthermore, the impact of using multiple electronic chips having the same volume and power of one chip on its cooling and the process of heat transfer is investigated. A complete three-dimensional transient mathematical model for the studied physical model is introduced and solved by utilizing a finite difference numerical method. Experiments are conducted to validate the numerical solution which shows good agreement between experimental and numerical results. Findings show that neglecting radiation between cavity walls increases chip temperature by approximately 20 %. The best electronic chip position achieves minimum chip temperature when it is installed at the center of the cavity base plate. Using two and four electronic chips having the same volume and power of one chip decreases the flow eddies inside the cavity and the maximum temperature of one chip by about 25.3 % and 42.6 %, respectively.