Are you in a hot environment?
Is the phone connected to a charger?
What sort of games are these?
Do you have other processes running actively? (Maybe check your battery consumption stats).
What do you mean by "hot"?
Has this changed recently, or has it always been like this?
Running a camera and playing some games (especially those with advanced graphics, those using the camera and a network connection) are some of the activities which generate the most heat. If you are already in a hot environment, or if this is in addition to other sources of heat (e.g. charging) then the phone can get hot quickly. But it's very hard to say whether what you observe is abnormal or not, because "becomes hot" means different things to different people. Could you check the battery temperature (many system info or battery monitor apps can do that)?
And if it is abnormal, unfortunately it may not be easy to identify the cause, which is why I asked that list of questions above.
