There is no doubt that the use of microwaves kills insects, but for termites it is really effective only for drywood termites. I tend to put my greatest faith in the opinions of unbiased experts, which really means the University researchers who test these devices using a proper protocol to establish realistic results and conclusions. A lot of termite companies are now using microwave technology, but my cynicism tells me that sometimes this use does not necessarily mean effectiveness. The University of California has tested microwaves for drywood termites and one conclusion they offered was that it typically gave from 89-98% control of the termites in a structure. That seems like a lot, but leaving 5-10% of the termites behind, perhaps alive and well, means that the problem still exists. 

The limitations several University websites offer are these. Some locations in any structure are going to be very difficult to access, and getting the microwaves to those locations at a level high enough to heat up that wood to a lethal level may be nearly impossible. Within hidden areas there may be heat "sinks" that prevent the temperature within the wood from getting to the lethal level. Depending on the power level of the device there is a chance that some surface damage may occur. And, since the microwaves are going to heat up only the wood where the device is directed it is treating only small sections at any one time. This is okay if the entire infestation is located in that small area of wood, but as we know, drywood termites have small colonies, and numerous separate colonies could exist within a structure. If they are not all detected and treated, killing one of them and leaving others that were unknown at the time of treatment leads to continued termite presence. 

But, just like other local treatments that might replace the use of insecticides or fumigants, microwaves have a place. Not only are they effective when used properly but they offer the choice of an alternative to toxins for those customers who prefer it.