      P. Calvani 1 , M.C. Rossi 1 , G. Conte 1 , S. Carta 1,2 , E. Giovine 2 , B. Pasciuto 3 , E. Limiti 3 , F. Cappelluti 4 , V. Ralchenko 5 , A. Bolshakov 5 , G. Sharonov 6 1 Electronic Engineering Dept., Roma Tre University, Roma, Italy 2 IFN-CNR, Roma, Italy 3 Electronic Engineering Dept., Tor Vergata University, Roma, Italy 4 Department of Electronics, Politecnico di Torino, Torino, Italy 5 General Physics Institute, Russian Academy of Science, Moscow, Russia 6 Institute of Applied Physical Problems, Belarus State University, Minsk, Belarus  Epitaxial diamond films were deposited on polished single crystal Ib type HPHT diamond plates of (100) orientation by microwave CVD. The epilayers were used for the fabrication of surface channel MESFET structures having sub-micrometer gate length in the range 200-800 nm. Realized devices show maximum drain current and trasconductance values of about 190 mA/mm and 80 mS/mm, respectively, for MESFETs having 200 nm gate length. RF performance evaluation gave cut off frequency of about 14 GHz and maximum oscillation frequency of more than 26 GHz for the same device geometry.  Current semiconducting materials do not offer high power RF (> 8 GHz) devices in simple solid state device configurations, required for compact MMIC usually employed for communication and radar applications. Among wide band gap materials, diamond has by far the optimum material characteristics allowing for, at least in principle, the best power amplification per unit gate length at microwave frequencies, to be employed in the fields of electrical power management and wireless communications. Owing to the encouraging high frequency and power performance, the technology of hydrogenated diamond is currently receiving much interest for the fabrication of surface channel metal semiconductor field effect transistors (MESFETs) [1-3]. In this structure, hydrogen termination of diamond together with carrier transfer into surface acceptor states promotes an upward surface band bending which gives rise to a space charge extending several nanometers below the surface without the addiction of extrinsic doping impurities. Here holes are confined perpendicularly to the surface from the electrostatic field arising from the charge separation (positive charge in diamond and negative on the surface acceptors) whereas are free to move in parallel to the surface [4], where they form a 2DHG closely following the surface topography. In this way, surface hole densities up to 10 13 cm -2 and mobility values about 100-200 cm 2 /Vs cm -2 are typically achieved [5]. In this context, two different strategies are currently pursued for surface channel device realization, based on polycrystalline and on single diamond substrates. In the former case large substrates required for electronic applications are already available, although achieved results still appear to be affected by the polycrystalline sample structure. At variance, the Mater. Res. Soc. Symp. Proc. Vol. 1203 © 2010 Materials Research Society 1203-J15-03