text: A conductor has constant electric potential(under electrostatic conditions). This means that the electric field inside the conductor is  always zero.( E=-gradV)\nNow, draw a Gaussian surface which lies entirely in the conductor. By Gauss's Law, the net charge inside this surface must be zero (since E is zero and hence flux crossing the surface is zero). This is true for any other Gaussian surface *entirely inside* the conductor. Hence charge must be on the surface of the conductor.\nThis is one of the ways to *understand* the phenomena but I guess it does not give the *reason*!