Heat transfer from a constant-temperature surface in the two-dimensional, steady free-stream, adverse-pressure-gradient separating turbulent boundary layer of Simpson et al. (1981 a,b) was studied experimentally using a constant-current resistance thermometer and a fast response thin-layered surface heat flux gage. Upstream of the incipient detachment (ID) location (1% backflow), the Stanton number St obeys the attached flow correlation recommended by Moffat and Kays (1984). Downstream the St vs. enthalpy thickness Reynolds number that is valid for zero and mild adverse-pressure gradient flows breaks down. The time-mean heat transfer decreases rapidly downstream of ID with a broad minimum near the location of time-mean detachment (50% backflow), which is approximately 30% below attached-boundary-layer levels. Downstream of the location of time-mean detachment, heat transfer increases rapidly. The surface heat transfer under the backflow region was correlated to large near-wall velocity fluctuations and is approximately described by the correlation of Maciejewski and Moffat (1992). The rms of surface heat flux fluctuations attain a maximum value near the location of time-mean detachment. Skewness and flatness factors of surface heat flux fluctuations increase to large values downstream of detachment because of the intermittently large heat transfer due to large-scale turbulent structures.