A preliminary survey of thermal electron temperatures in the late afternoon sector (1630--1800 hours magnetic local time) of the high-altitude ionosphere has been made up to 8000-km altitude with data from a spherical Langmuir probe onboard the polar-orbiting satellite S3-3. The temperature of the thermal electrons is found to be almost independent of altitude along closed field lines above ~3000 km when both ends of the magnetic field pass through a sunlit ionosphere at 300-km altitude. Over the sunlit polar cap, a temerature gradient of ~0.4 ¿K/km is observed up to 5000-km altitude. The temperature of the thermal electrons at high altitudes is found to have a dependence on invariant latitude similar to previous observations near 1000-km altitude.