Abstract We characterized OH-terminated diamond (111) surfaces which show step-terrace (ST) and bunching-step (BS) regions from contact potential difference (CPD) and current to investigate the relationships between surface topography and generation of interface states on the surfaces. The OH-termination was performed using water vapor annealing. The CPD and current measurements were conducted by conductive-probe AFM and Kelvin-probe force microscopy. The CPD and current were highly correlated with the surface topography. The I–V characteristics shows typical ideality factors (n) of about 1.5 and 2.0 in the ST region and the BS region, respectively. As the n were higher than that of an ideal Schottky contact (n = 1.0), we concluded that a metal insulator semiconductor diode structure, whose n increases as its interface state density increases, was formed. Considering that step density in the BS region was much higher than that in the ST region, the steps seemed to have generated the interface states.