A method of etching the trench portions of a thermal inkjet printhead using a robust mask that precisely defines the area of the substrate surface to be etched and that protects the adjacent drop generator components from damaging exposure to the silicon etchant. The process in accordance with the present invention uses as a mask some of the material that is also used in patterned layers for producing the drop generator components on the substrate. The placement of the mask components on the substrate occurs simultaneously with the production of the drop generator components, thereby minimizing the time and expense of creating the silicon-etchant mask.