© 2017 Elsevier B.V. Normally-on (depletion mode) and normally-off (enhancement mode) diamond Junction Field Effect Transistors (JFETs) have been analyzed by means of a commercially available TCAD software. First, the parameters used for describing the incomplete ionization, avalanche, and mobility models in diamond have been discussed and assessed against the state-of-the-art. The on- and off-state electrical characteristics of diamond JFETs have been simulated with the suggested parameter values and matched with a set of available experimental data. Secondly, an optimization technique which can improve the performance of an enhancement mode diamond JFET that operates in the unipolar conduction regime has been proposed. This method takes into account the unique properties and limitations of diamond and highlights the main issues that can arise from the design of a normally-off diamond JFET. In particular, the crucial effect of the high temperature on the performance of the normally-off JFET has been investigated. The adopted technique is mainly based on a design of TCAD experiments and no mathematical algorithms have been developed for the calculation of the optimized set of parameters.