The authors attempted to grow a semi-insulating 4H-SiC epitaxial layer by in situ vanadium doping. The homoepitaxial growth of the vanadium-doped 4H-SiC layer was performed by metallorganic chemical vapor deposition using the organosilicon precursor bis-trimethylsilylmethane (BTMSM, C7H20Si2) and the metallorganic precursor bis-cyclopentadienylvanadium (Verrocene, C10H10V). The vanadium doping effect on the crystallinity of the epi layer was very destructive. Vanadium-doped epi layers grown under normal conditions had various crystal defects such as micropipes and polytype inclusions, but this crystallinity degradation was overcome by elevating the growth temperature. For measurement of the resistivity of the highly resistive vanadium-doped 4H-SiC epi layers, the authors used the on-resistance technique. Based on the measurements of the on-resistance of the Schottky barrier diode fabricated using the vanadium-doped epi layers, it was revealed that the residual donor concentration of the epi layers was decreased with increasing partial pressure of verrocene. The resistivity of the in situ vanadium-doped 4H-SiC epi layer was about 10(7)-10(12) Omega cm. (c) 2007 The Electrochemical Society.