Dynamics Explorer-2 is permitting the first measurements of the global structure of the F-regions at very high levels of solar activity (S¿>200). Selected full orbits of Langmuir probe measurements of electron temperature, Te, and density, Ne, are shown to illustrate this global structure and some of the ionospheric features that are the topic of other papers in this issue. The ionospheric thermal structure is of particular interest because Te is a sensitive indicator of the coupling of magnetospheric energy into the upper atmosphere. A comparison of these heating effects with those observed at solar minimum shows that the magnetospheric sources are more important at solar maximum, as might have been expected. Heating at the cusp, the auroral oval and the plasma-pause is generally both greater and more variable. Electron cooling rate calculations employing low latitude measurements indicate that solar extreme ultraviolet heating of the F region at solar maximum is enhanced by a factor that is greater than the increase in solar flux. Some of this enhanced electron heating arises from the increase in electron heating efficiency at the higher Ne of solar maximum, but this appears insufficient to completely resolve the discrepancy.