An experimental study of fluid flow and heat transfer has been carried out for jet impingement cooling on a semicircular concave surface. The distributions of mean velocity and velocity fluctuation on the concave surface have been measured in free, impinging and wall jet how regions by using a Laser Doppler Anemometer. Local Nusselt numbers have also been measured. Variations of jet Reynolds numbers, the spacing between the nozzle and the target and the distance from the stagnation point in the circumferential direction have been considered. Emphasis has been placed on measuring turbulent jet flow characteristics including impinging and evolving wall jets and interpreting heat transfer data, particularly, the occurrence and its location of secondary peak in connection with data of measured mean velocity and velocity fluctuations on the concave surface. (C) 2000 Elsevier Science Ltd. All rights reserved.