In the context of a growing need for power semiconductor devices, as more and more applications from motor drives to power grids requires DC/AC, AC-DC or DC-DC converters with higher efficiencies and higher power densities, the research on new solutions is essential. Wide band gap materials have already shown their superior physical properties for this kind of applications, due to their ability to sustain larger current power densities and voltages compared to silicon based devices. Amongst them, diamond is an ultra-wide band gap material (5.5 eV) with one of the highest critical electric field capability , which coupled with its great thermal conductivity (22 W/cm.K) and hole mobility (2000 cm²/V.s) makes it a particularly interesting semiconductor for power electronics. Despite the challenging fabrication of diamond based devices due to the small standard substrate size (a few mm²), diamond is still being actively studied with constant progresses.This thesis is focused on the design , fabrication and characterization of diamond Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) which takes advantage of the wide band gap of diamond to design an original device architecture based on a stable deep depletion regime. The design optimization of such devices will be established according to the state of the art physical models, then experimental test devices will be analysed to better understand the physics of the diamond MOSFET. Finally, a performance evaluation in comparison to other semiconductors and existing diamond devices will be presented. Several perspectives from these performances as well as from original architectures specific to diamond will be drawn.