Abstract Carrier transport mechanisms at p-diamond/metal interfaces were studied by analyzing the dependencies of the specific contact resistivities ( ρ c ) on the measurement temperature and the acceptor concentration ( N A ). A variety of metals, such as Ti, Mo, Cr (carbide forming metals), Pd and Co (carbon soluble metals), were deposited on boron-doped polycrystalline diamond films, and the ρ c values were measured by a transmission line method. A constant Schottky barrier height (SBH) of around 0.5 eV was measured for these annealed contacts, and the reason was believed to be due to phase transformation from metastable diamond to a stable conductive graphite layer in the vicinity of the diamond/metal interface. By controlling the crystal structure at the diamond/metal interface, non-annealed ohmic and high-voltage Schottky contacts were successfully developed.