Abstract: A photo-mask to be used in a light exposure step for manufacturing semiconductor devices is cleaned by wetting front and rear surfaces of the mask with a liquid, brushing the wetted surfaces with a pair of rotary brushes, wetting the brushed surfaces with an electrolytic solution containing sufficient electrolyte to substantially eliminate electrostatic charge from the surfaces, spraying and immersing the photo-mask in an organic liquid such as an alcohol, and then drying the photo-mask.

Abstract: An organic coating with slits or holes in a predetermined pattern is disposed on the surface of an electrically insulating substrate on which electrode leads have been formed. A paste of an electrically resistive material fills the slits or holes and is dried at 120.degree. to 140.degree. C. The surface of the paste is flush with that of the coating after which the paste preliminarily baked in a stream of oxygen at 500.degree. to 600.degree. C. while the coating is burnt off. The paste is fully baked at 800.degree. to 1000.degree. C. to form a heating resistor elements.