Surface transfer doping is demonstrated on hydrogenated diamond (100) by the electron acceptor, tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). Synchrotron-based photoemission spectroscopy reveals that electrons are transferred from diamond to adsorbed F4-TCNQ, leaving a diamond surface p-type doped with a high areal density of holes of about 1.6 x 10(13) cm(-2).