My iPhone 4S gets really hot when charging and sometimes when I use it.

Hello satishmunde14,

Thanks for the question. The following resource provides some information about temperature:

iOS devices: Keeping device within acceptable operating temperatures

http://support.apple.com/kb/HT2101

When using the device or charging the battery, it is normal for it to get warm. The exterior of the device functions as a cooling surface that transfers heat from inside the device to the cooler air outside.

By all means, if you believe the temperature is a concern (along with the battery life), you can isolate the issue by restoring your device as new:

iOS: How to back up your data and set up your device as a new device

http://support.apple.com/kb/HT4137

Thanks,

Matt M.