Mesa etched transmission line model (TLM) test structures with different contact lengths have been fabricated on heavily boron doped polycrystalline diamond films. The behavior of the contact and contact end resistance measurements can be fully explained using the TLM. No influence of the grain size on the contact resistivity has been observed. High surface boron doping concentrations led to low contact resistivities, in agreement with numerical calculations. Annealing of Al/Si–diamond contacts at 450 °C in N2leads to lower contact resistivities due the formation of SiC at the metal–diamond interface. The temperature dependence of the specific contact resistivity can be described well with a tunneling model before annealing. After annealing no useful fit is possible, indicative of the fact that the SiC interface layer acts as defect layer. ©1996 American Institute of Physics.