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 °C 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.