Laterally microstructured devices suitable for applying high electric fields above approximate to 10(6) V/cm have been fabricated on homoepitaxially grown chemical vapor deposited (CVD) diamond thin layers using a focused ion beam (FIB) technique with 30 keV Ga ions. Characteristic regions of the microstructure fabricated on the undoped diamond were found to clearly change only after a high electric field greater than or equal to 1 x 10(6) V/cm was applied to a non-implanted narrow volume. An energy-dispersive X-ray (EDX) analysis confirmed that substantial Ga accumulations occurred mainly in the positively-biased region to which approximate to 10(18) Ga ions/cm(2) were implanted to form graphitized (conducting) layers. A similar phenomenon was also observed in the graphitized region adjacent to the positively-biased side of the parallel thin graphitized layers both of which sandwiched the field-applied volume. This phenomenon clearly verifies that implanted Ga ions can easily diffuse in the graphitized layer having substantial amounts of lattice defects under the presence of hot carriers created in such high electric fields. The present FIB fabrication process combined with a newly developed Ga removing process demonstrates the possibility for realization of high electric field-compatible diamond devices with graphitized (metallic) areas to a submicron accuracy. (C) 2003 Elsevier Science B.V. All rights reserved.