In this work, fluid flow and heat transfer characteristics of three-dimensional (3D) wall jets exiting from a circular and square opening are presented based on experimental investigations. Two hydraulic diameters, namely, 2.5 and 7.5 mm and a Reynolds number range of 5000–20,000 have been considered. Mean velocity and turbulence intensity distribution in the walljet are quantified using a hot wire anemometry. Measurements are done both along the streamwise and spanwise directions. Transient infrared thermography is used for mapping the temperatures over the surface, and the heat transfer coefficients are estimated using a semi-infinite approximation methodology. Results show that, for circular jets, the effect of the jet diameter on the local and the spanwise-averaged Nusselt number is most pronounced near the jet exit. Further, it is also observed that circular jets have an edge over square jets. A correlation with a high correlation coefficient of 0.95 has been developed for spanwise average Nusselt number as a function of the Reynolds number and the dimensionless streamwise distance.