The 680 µm thick wafer is back-etched, leaving the thin film 3C-SiC as the flexible diaphragm to detect pressure. The etching processes are performed with three different KOH concentrations (35, 45 and 55 %), without and with 10 % IPA surfactant and the etching temperatures of 50 and 80 °C. Graphs are plotted on the effect of the etch rate and etch depth against these three parameters. In addition, the surface roughnesses of the diaphragms at these conditions are measured, photographed and analyzed. The results show that the back-etching of a 3C-SiC-on-Si wafer is fastest at higher temperature and KOH concentration and without IPA surfactant, but at the price of higher surface roughness. The addition of 10 % IPA reduces the surface roughness significantly. We also notice the increasing presence of micro-pipes at higher KOH concentration and etching temperature. The experiments are performed using bulge test method that induces the effects of dimensional layout diaphragm of 2,000 and 2,500 µm, the curve shows a good resemblance each other at pressure of 5.0 MPa. The maximum difference linearity of 2,000 and 2,500 µm is 98.7 and 97.1 %, respectively. It is revealed that the small layout dimensional can sustain the diaphragm at high pressure compare with large dimensional layout of 3,000 and 3,500 µm with the linearity is about 73.2 and 62.6 %, respectively.