New applications for porous SiC are shown. They include using porous SiC substrate with introduced Mg for autodoping of GaN films grown on 6H-SiC, and fabricating semi-insulating 4H-SiC films through doping porous SiC with Si or V. In the latter cases, specific resistivity of 10(11) and 10(12) Omega.cm at 500K was achieved, respectively. In all cases, the diffusion was found to be the driving force for the effective doping.