The cooling process of a semi-circular sheet simulating the leading edge of the gas turbine blade has been investigated experimentally in the present study. The circular surface is subjected into a five impinging air jets with variable diameter cases at a Reynolds number ranged from 5,000 to 40,000. The diameter of the orifice is varied between three configurations namely, Fixed Diameter case, Ascending Diameter case (AD), and Descending Diameter case (DD). The surface temperature has been investigated using Infra-red thermal camera, which provides thermal images of the surface. The results of temperature contours and local heat transfer coefficient have been discussed for the study parameters. The results state that the sides of the sheet that far from impingement gets higher temperature while the area beneath the impingement gets the higher cooling rates. For FD configuration, the stagnation heat transfer coefficient of the first jet is the highest while the lower case is achieved under the last jet. The stagnation heat transfer coefficient decreases significantly in the flow stream direction for the DD case and it increases in case of AD due to the non- uniform impingement flow.