The invention relates to a method of manufacturing a field-effect transistor, especially a chemical sensitive field-effect transistor applied for a gas sensor. A grid insulation protective layer (3) is applied in the method in order to improve the adopted processing technology and enhance the possibility of changes in the number of materials and the substrate processing sequences. The grid insulation protective layer (3) is applied for protecting a grid insulation layer (2) from being impacted by the surroundings in a further processing procedure and partially or completely removed before a grid layer is finished. Furthermore, the invention relates to a field-effect transistor and the application thereof.
