We have had the same types of problems with my son (almost 6). Here are some things that we have done that have helped:

1. Reward Chart: Pick something he really wants and draw it on a piece of paper and hang it on his bedroom door. Make 3 circles and allow him to place a sticker in the circle if he stays in his bed. When he fills the circles he gets the prize. If this works for him start making him do more days or consecutive days before earning the prize.

2. Even if he comes in your bed place him back in his when he falls asleep so he becomes used to being in his own bed.

3. Make a bedtime (visual) schedule (snack, brush teeth, story, pray, bed).

4. Talk about other kids that stay in their bed and that they are fine

5. Praise all efforts

6. Keep putting him back in his bed if he gets up, don't make it fun or talk, just walk him back to his room

7. Lock your door.

Hang in there...