will their be a season 4 to highschool dxd
maybe, maybe not
Books say yes. Sales say probably not. Who knows though, it is a fairly popular series so it very well could get a follow-up.
In other words: no announcement has been made. Our best hope would be sometime next year for an announcement probably.
This question was already answered in the official FAQ. Question #10, to be exact:
As such, this topic will now be locked.