Electrical properties were investigated for nitrogen-doped SiC, prepared by pressureless sintering (by adding boron and carbon as the sintering additives). A nitrogen doping process compensated the acceptor level that was formed by solid-dissolved boron, one of the sintering additives. Thus, it was confirmed that the donor level was formed by solid-dissolved nitrogen. The specific electrical resistance of nitrogen-doped pressureless sintered SiC was clearly separated into two groupings. One grouping of electrical properties strongly depended on the temperature, while the other grouping of electrical properties was less dependent. Microscopy, electron diffraction, and X-ray diffraction analyses suggested that the electrical conduction through a dominant 6H α-SiC crystal phase, where a nitrogen-doped donor level is deep, the temperature dependency is strong. On the other hand, the electrical conduction through a dominant 3C β-SiC crystal phase, where a nitrogen-doped donor level is shallow, the dependency on temperature is less pronounced. Two sintered SiC samples were prepared by using the recrystallizing technique. One only consisted of a 6H α-SiC crystal phase, and the other only of a 3C β-SiC crystal phase. The experimentally measured electrical properties showed agreement with the above stated theory interpretation.