Film cooling, along with other approaches, are essential to control the very high gas temperatures passing over gas turbine blades. The abundant research in film cooling characteristics and parameters reveals the importance of the topic as an integral part of blade cooling. Although these extensive studies have identified the important parameters that influence both aerodynamics and thermal performance of film cooling, optimization research is continuing to enhance overall system design. Owing to the simplicity in manufacturing, the circular hole shape has been studied more than any other shaped coolant hole. However, data from literature shows that shaped hole may limit coolant jet separation, resulting in less aerodynamic losses and better cooling effect. The purpose of the present study is to numerically verify aeroslot (rectangular slot with fully round ends) superiority over circular one by neutralizing other important parameters, and to optimize the aeroslot aspect ratio (straight length over thickness) to maximize cooling effect. After confirming model validity, a comparison between aeroslot and circular hole showed a superiority of the former in terms of adiabatic film effectiveness. In addition, aspect ratio optimization was evaluated in terms of both adiabatic film effectiveness and Nusselt number indications. Aspect ratios from 2.5 to 8 were tested. It was found that the optimum aspect ratio for overall cooling performance is 7. The influence of velocity and thermal diffusion on surface temperature was examined.