Intrinsic diamond with a bandgap of 5.4 eV exhibits a surface conductivity (SC) of the order of 10(-5) Omega(-1) when terminated by hydrogen. This conductivity is carried by a hole-accumulation layer close to the surface with an areal carrier concentration of about 10(13) cm(-2), and it has already been utilized for a unique kind of field effect transistor [H. Kawarada, Surf. Sci. Rep., 26, 205 (1996)]. Although the microscopic doping mechanism is still under debate. Based on the results of a variety of surface-sensitive experiments we propose a new surface-transfer doping mechanism by which electron transfer from the valence band to adsorbed, hydrated ionic species at the surface creates the holes for the surface conductivity. In order to draw a complete picture of the surface conductivity concepts from surface and semiconductor physics as well as electrochemistry have to be adopted. (C) 2004 The Electrochemical Society.