Three novel hexagonal Si-C-N structures, namely SiC 3 N 3 , SiC 7 N 6 , and SiC 13 N 14 , were constructed on the basis of the α-Si 3 N 4 crystal structure. The stability of the three structures is demonstrated by analyzing their elastic constants and phonon dispersion spectra and by calculating their formation energies. The calculated band structures and partial densities of states suggest that the SiC 3 N 3 and SiC 7 N 6 structures possess hole conductivity. The electron orbital analyses indicate that the SiC 3 N 3 and SiC 7 N 6 crystals possess three-dimensional and one-dimensional conductivity, respectively. SiC 13 N 14 is a semiconductor with a wide bandgap of 4.39 eV. Based on two different hardness models and indentation shear stress calculations, the Vickers hardness values of SiC 3 N 3 , SiC 7 N 6 , and SiC 13 N 14 are estimated to be 28.04/28.45/16.18 GPa, 31.17/34.19/20.24 GPa, and 40.60/41.59/36.40 GPa. This result indicates that SiC 3 N 3 and SiC 7 N 6 are conductive hard materials while SiC 13 N 14 is a quasi superhard material.