It can be multiple things.
- A faulty battery
- Your external sd card (try removing it)
- An app that is constantly using your cpu.
What is overheating? My phone gets hot sometimes, but not like really really hot.
Samsung Galaxy S 4 I9505 | WanamLite v2.6
Samsung Galaxy S II I9100 : AOKP 4.2.1
HTC Touch Pro2 | ROM: Valkyrie 6.5.23115TR2.5
HTC HD2 | DarkStone1337 [FroyoStone Sense - V3.2]
HTC Desire : Oxygen v2.1.3