To fabricate semi-insulating SiC bulk crystals, vanadium doping was performed by adding vanadium as a solid source to the SiC starting material. Electrical and optical properties of the PVT grown crystals were investigated. The nitrogen concentration up to about 2 x 10(18) cm(-3) in the crystal areas near the seed as well as the maximum solubility of vanadium in SiC of about 5 x 10(17) cm(-3) are limiting yield and electrical homogeneity of vanadium doped SiC bulk crystals. Depletion of vanadium during growth can be prevented by lowering the growth temperature or using an inner container filled with a SiC/VC-mixture leading to a homogeneous vanadium incorporation in the crystals. Co-doping of vanadium and boron was successfully performed to attain SiC crystals with a fermi level close to mid-gap, leading to thermal activation energies up to about 1,7 eV. The V3+ and V4+ charge states of vanadium can be detected separately using optical absorption or electron spin resonance (ESR). With these techniques the electrical domination of the V3+/V4+ acceptor or the V4+/V5+ donor level in V doped samples can be determined.