We investigated the effects of SiNx interlayers on the structural and electrical properties of nonpolar a-plane (11-20) GaN grown on r-plane (1-102) sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The Nomarski optical microscope images showed that the deposition conditions of the SiNx layer could strongly affect the aplane GaN surface morphology due to the different SiNx coverage. Basal-plane stacking faults (BSFs) and threading dislocation (TD) densities were reduced in the a-plane GaN samples with high SiNx coverage and multiple SiNx-treated GaN interlayers. These results indicate that TD reduction is associated with an increase in the 3D growth step and with the blocking of TD propagation. From on-axis (11-20) X-ray rocking curve (XRC) measurements, the anisotropy of full width at half maximum (FWHM) can be attributed to the crystal mosaicity due to insertion of different SiNx interlayers. The anisotropy of sheet resistance between the c-and m-axis was also clearly seen in a-plane GaN samples with a high density of defects, which was attributed to the BSFs as scattering centers.