Early last fall I first noticed what appeared to be sawdust around the base of a tree beside my driveway, then further up there were a series of holes in a straight line around the trunk. Carpenter ants were building a new nest in that tree. I sprayed them with Wasp & Hornet killer which was handy and worked, used the whole can. There were so many dead ants, they made a black ring about a foot wide around the tree base.

Here is a link that might be useful: Carpenter Ants

First thing, are you sure they are carpenter ants?

I had a carpenter ant problem when I bought my house. The thing with them is they are hard to get rid of if you don't get rid of the main nest. They like to set up satellite nests in your house. For me, it turned out that there was an old oak tree that they were nesting in and when that was removed it took care of the problem. The tree was probably 150 years old and hollow the whole way up and to around 3 feet below ground.

It's a good idea, especially if you live in the country to spray your foundation once or twice a year to keep the bugs out. Another step I take is to lay down some diatemaceous earth as a barrier around the house.

It's a tough call whether to call in an exterminator, because some of the bigger national companies are only going to do enough to try to keep you content, while still keeping you coming back so they can sell you another contract. If the foundation spray and DE barrier don't work, you may try to find some local smaller company to come instead of the big national chain.