  We have investigated the structure and evolution of hot gas in the 30 Dor
nebula, based on recent X-ray observations. Our deep ROSAT HRI image shows that
diffuse X-ray emission arises in blister-shaped regions outlined by loops of
HII gas. X-ray spectroscopic data from ASCA confirm the thermal nature of the
emission and indicate that hot gas temperature decreases from the core to the
halo of the nebula. The structure of the nebula can be understood as outflows
of hot and HII gases from the parent giant molecular cloud of the central OB
association. The dynamic mixing between the two gas phases is likely
responsible for the mass loading to the hot gas, as required to explain the
observed thermal structure and X-ray luminosity of the nebula. Such processes
should also be important in the formation of similar giant HII regions and in
their subsequent evolution into supergiant bubbles or galactic chimneys.
