I think the median average temperature is around 2,100°C.

The Earth has a radius of 6,371km, giving a volume of 1.08e13km^3^.

A sphere of half this volume would have a radius of 5,057km. Within the Earth, this sphere would sit at a depth of 6,371 - 5,057 = 1,314km.

From this chart, the temperature at that depth is around 2,100°C, so half the volume of the Earth has a temperature above that, and half a temperature below it