Abstract This work presents a study on the mechanism of injection and charge transport through a CVD diamond/n + -Si interface. The current–voltage–temperature characteristics of CVD diamond/silicon heterojunctions measured in the temperature range 119–400 K have been interpreted according to thermionic theory and thermionic field-emission theory. This junction shows deviations from the ideal thermionic theory current model, suggesting the presence of surface states, thin-layer depletion and/or non-homogeneity in the diamond/silicon interface. The T 0 anomaly has been used to explain the behaviour of the ideality factor with temperature. At very low temperatures tunnelling may occur because the E 00 values for these junctions are close to the value expected by thermionic field-emission theory. The usual activation-energy plot deviates from linearity at low temperatures. This deviation has been corrected supposing a ln( J S / T 2 ) versus 10 3 / nT plot. Under these conditions the Richardson constant is found to be 0.819 A cm −2 K −2 , which is close to the theoretical value of 1.2 A cm −2 K −2 . Field-emission device is a promising application for diamond/silicon structure.