The (100) and (111) crystalline cubic silicon nitride (3C-SiC) thin films have been epitaxially deposited on (100) silicon substrate with the thickness of 0.5 µm and 1.0 µm. The effects of the different growth of 3C-SiC are considered as the most critical factor in determining the mechanical properties by comparing with bulk value such as Young’s modulus (~455 GPa) and hardness (~42 GPa). This paper evaluates the mechanical characteristic of the 3C-SiC-on-Si wafers to improve the 3C-SiC thin film quality. The aim is to employ the thin film as the flexible diaphragm in the MEMS capacitive pressure sensor for extreme environment. The surface morphology of thin layer of grown 3C-SiC wafers are characterized by X-ray diffraction (XRD), Infinite Focus Microscopy (IFM), scanning electron microscopy (SEM) and nano-indentation test. The results show the superior mechanical strengths of both (100) and (111) 3C-SiC thin films over (100) Si. To conclude, these results show that (100) and (111) 3C-SiC are indeed high quality thin film mechanically compare to (100) Si thin film, and is suitable to employed as the flexible diaphragm of the MEMS capacitive pressure sensor for extreme environments.