The only way to successfully get rid of them is to get an exterminator in who will spray and treat twice, usually 6 weeks apart. We were told they hold the most eggs and don't need food or anything to survive as they eat their own feces and shed shells etc. Each egg they have contains something like 400 babies and they are able to breed from quite young. They like warm & moist areas so are usually found in kitchens, bathrooms and laundries.
We're about to get the exterminators in to our house again to just keep on top of it. I wouldn't suggest getting a new microwave until they have been treated or they will just find their way into the new one. Good luck. They're disgusting things!