Why does the debugger show 0xFFFFFFFF as the value for sbyte?

After entering the negative value, say -1 into the sbyte variable, the debugger shows the value 0xFFFFFFFF - 4 bytes:

After conversion to a larger type of Int32, the value will remain 0xFFFFFFFF. Why is not this 0x000000FF?

In the case of positive values, sbyte stores only 1 byte.