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The growth of high-quality AlN films has always been the focus of research. Combined with NH 3 in situ pretreatment before growth, with optimized growth conditions, we demonstrated a periodic growth method, which alternates between three-dimensional (3D) growth mode and two-dimensional (2D) growth mode, to grow a thick crack-free AlN film with good crystal quality on the on-axis 4H-SiC substrate by metal− organic chemical vapor deposition (MOCVD). X-ray rocking curves (XRCs) indicated that full width at half-maximum (FWHM) of the ( 0002) and (10−12) reflections were 241.3″ and 474.4″, respectively. The film thickness was over 1.4 μm. Lattice constant and residual stress results showed residual compressive stress in the sample. The periodic two-step growth and substrate pretreatment both play an important role in controlling the residual stress of films to avoid cracking. This work can serve as an important reference for growing high-quality crack-free AlN on SiC.