Dimpled surfaces may be considered for heat transfer enhancement in internal cooling of gas turbine airfoils. In this study, convective heat transfer and pressure drop for turbulent airflow in a square channel with a dimpled wall were examined. Experiments were conducted to determine the average heat transfer coefficient on the dimpled wall and the overall pressure drop across the channel, for nine concave and cylindrical dimples with various diameters and depths, and for Reynolds numbers (based on the channel hydraulic diameter) between 10,000 and 65,000. For the concave and cylindrical dimple configurations studied, the dimples were found to enhance the heat transfer coefficient by 70% (1.7 times) to over three times the value for fully developed turbulent flow through a smooth tube, with increase of the overall pressure drop of over four times. For both the concave and cylindrical dimples, heat transfer was enhanced more when the dimples covered a larger portion of the surface of the wall. The cylindrical dimples caused higher overall heat transfer coefficient (based on the projected area) and lower pressure drop than the concave dimples with the same diameters and depths. Thus, cylindrical dimple configuration may be a better alternative than concave dimples in enhancing heat transfer, for the experimental conditions and dimple configurations investigated. Further experiments are recommended to determine if cylindrical dimples of other dimensions also give higher thermal performances than concave dimples of the same dimensions, subjected to other flow and thermal boundary conditions, such as irregular channels with or without rotation.