Contact Samsung by opening the Members app, go to Support on the bottom right corner and scroll untill you see Error Report. Click on it and follow the steps
Is it hot all the time or only when charging? Charging will cause the battery at times sometimes causes the battery to heat up. Check the battery usgae, maybe there is an app running in the background that is consuming more power cauising it.
An application you installed might be incompatible with your phone or not optimized. If you don't want to take it in, I'd suggest formatting the device and installing applications individually. If you take it into a repair store, they can identify the application for you or, like someone else asked, if this happens during charging, it's normal.
Do a complete software reinstall, run it bear bones for a bit, and see if the issue persists, maybe someone else has a different suggestion if you don't want to go this route.
