[AC Question]

Technically we all have same problem and no one has solution for it.
I have 2 mobile S5 and grand 2. Grand 2 is okay its get hot only when I plugged in charging and playing games. But my S5 get heat up too much, whenever I download file which take more than 20min, when I play good graphic game, using mob for longer time. Now I think this is negative side of s5 which company completely ignored.

[B. Diddy]

Welcome to Android Central! What do you mean by downloading a file that takes more than 20 minutes? A file should never take that long--is it freezing during the download?

The S5 and the Grand 2 are significantly different devices, so you can't really compare the two directly. The S5 has a significantly more powerful SoC, and has a higher resolution screen, both of which use more power (especially when the device is doing something processor intensive, like playing a complex game). More power means more heat generated.

That's not to say that a phone should get hot enough that it gets uncomfortable. Can you measure how hot it's getting? There are a number of apps that can give you CPU and battery temps.