While using the iPhone 6s and 6s Plus, some users found that the Touch ID Home Button grew very hot all of a sudden. The heat is concentrated in the Touch ID only because the rest of the phone seems to be at normal temperature. Some noticed that once it started heating up, the button stopped responding so you could not use the Home button to turn the screen on. Many found that the problem occurred right after they unplugged their device from charging, but some reported that it happened irrelevant of charging.
Solution 1: Force restart your device
Restarting the iPhone is the quickest way of solving the problem. Try restarting your device by holding the Home button and the Sleep/ Wake Button together for about 10 seconds till you see the Apple Logo. This can help in solving the problem temporarily.
Solution 2: Let the phone cool before you try to reset it
If you find that you cannot restart your phone then leave it to cool down. Once the button cools, then try to reset the device and check if it works.
Solution 3: Take your phone to Apple Care
If the button continues to remain unresponsive and it is not cooling down then take the phone to Apple Care and you may be able to get a replacement if your phone is under warranty.