i had this same issue with my 6yr old son. wake him up routinly every night maybe even 2 times a night. after a long time of doing this his body will get used to wakein at this time. and he will get up and go! it worked for me anyways. good luck! and if nothing works take him to the doctor!!! it could be a sign of something VERY serious
You have three options:
Wait for him to outgrow it - and hope he does.
Wake him up at least once, maybe twice a night, to pee until he starts waking up on his own. If you try this, wake him up at the same time each night so his body develops a rhythm.
Get an alarm that sounds when he starts to pee. You can find these on line - search for "wee alarm". The idea is to teach his brain to wake up when the body has to "go".