We have investigated the electron spin resonance of donors in bulk and thin film β-SiC at T = 10K to 40K. In both, two donor spectra are resolved; a three line spectrum associated with nitrogen on the carbon site and a broader line of unidentified origin. The observable hyperfine splitting decreases with increasing temperature due to a small valley-orbit splitting, in qualitative agreement with photoluminescence results. The lineshape has a significant lorentzian character even at the lowest temperatures, indicating exchange interactions with residual conduction electrons, possibly from a shallower donor. We find a lower concentration of both donors in the bulk material and a different temperature dependence of the lineshape for the two samples.