A lumped chip path can turn a temperature difference into exact heat-flow power. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Thermal resistance carries real units
The lumped thermal path has resistance 5 K/W and temperature difference 30 K.
Rth=5K/W
Temperature difference over resistance gives power
The checked heat-flow power is 6 W. This does not claim a distributed three-dimensional chip temperature field.