A diaphragm, the most important part of pressure sensor, was successfully fabricated by an electro-chemical etch-stop (ECES) technique. It was important to control the thickness of the diaphragm precisely. We compared characteristic results of diaphragms by electro-chemical etch-stop with those by time-control etch-stop (TCES). The 4 inch n-Epi/p-substrate with 16 +/- 1 mu m thickness was utilized because the thickness of the diaphragm fabricated by ECES is controlled by the thickness of Epi.. The etching of silicon wafer was carried out in the solution (25 wt% KOH) at 80 degrees C, using 3 electrode system with potentiostat. Proper voltages were applied to etch p/n-type silicon wafer after determined open circuit potential (OCP) and passivation potential (PP) of n and p-type silicon, respectively. Thickness of diaphragms fabricated by ECES was controlled in the range of 16 +/- 1 mu m while that by TCES was in the range of 16.1 +/- 2 mu m. The roughness of diaphragm was 52 +/- 5 angstrom. When the pressure of 50 kPa was applied on the pressure sensor using the diaphragm fabricated by ECES, the error rate was improved to +/- 10 mV. In the case of the error rate of pressure sensor using the diaphragm fabricated by TC was in the range of +/- 25 mV under the same condition.