Overheating

Hi, 3 day ago I recieved my Mi4c (3gb) and just after couple of minutes surfing on the net I realized, that the top of the phone is really hot (the bottom was normal). The next day I tried it with game - after just one or two rounds (about 2 minutes) phone got hot again - again at the same area. I downloaded some app and I looked at the temperature after running the game - it showed even 55 degrees Celsia. Is it faulty piece or is it just software issue, which can be fixed by different ROM ?

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