Do you know where they're coming in from? As in, did you find a door or window or crack where you see them following the pheromones from? If you do you can do the following:
1. Apply a barrier treatment. Something like Ortho Home Defense Max, anything that is applied wet but dries to create a barrier like OHDM which is cypermethrin. This makes it so when the ants actually traverse the barrier they die on contact.
2. The barrier treatment will kill any that make it to the barrier. Once you know where to place the barrier, follow from the barrier to the outside and apply an outdoor bait so that they die outside before they make it to the barrier. For this there are a million brands that sell the gel baits like terro but in a plastic housing that you can stake into soft dirt. I've found these tremendously effective. The first day or so you stake it in, the ants will be all over it and you can see them eating the gel. The next day they'll all be dead and the gel won't have a single ant around it because they took the gel back to the colony and died.