A method of manufacturing a sensor, the method including forming an array of chemically-sensitive field effect transistors (chemFETs), depositing a dielectric layer over the chemFETs in the array, depositing a protective layer over the dielectric layer, etching the dielectric layer and the protective layer to form cavities corresponding to sensing surfaces of the chemFETs, and removing the protective layer. The method further includes, etching the dielectric layer and the protective layer together to form cavities corresponding to sensing surfaces of the chemFETs. The protective layer is at least one of a polymer, photoresist material, noble metal, copper oxide, and zinc oxide. The protective layer is removed using at least one of sodium hydroxide, organic solvent, aqua regia, ammonium carbonate, hydrochloric acid, acetic acid, and phosphoric acid.