Hi T.,
My son was potty-trained at 3, yet it took him quite a while to be dry at night. Children's bodies develop at different rates, and he my still not be physically at the point where he can reliably wake up when the need comes at night. What we did is that we didn't make a big deal out of it, but we talked about how big boys don't need pull-ups at night, and complimented him every time he woke up with a dry diaper, and eventually one night of dry diaper turned into 2, 3, 4, and eventually he slept without, with only an occasional accident. Also, it helps if you make sure that he drinks as little as possible in the 1.5-2 hours before going to bed.
Good luck! He'll get it, they all do.