Energy saving on a semiconductor fab is a big issue from the cost reduction point of view. This paper summarizes some effective actions carried out in our fab. We found that lowering the temperature setting in the make-up air unit (MAU) outlet can save as much as NT$ 5.6 million per year. Adjusting the amount of exhaust of processing equipment to a reasonable level can also reduce large amounts of the running cost. Furthermore, adding heat recovery coils into a traditional MAU can reduce both cooling load and heating load. All the energy-saving actions can serve as valuable references to other semiconductor fabs.