A method for surface treatment of a substrate is described in which a gas discharge at or about atmospheric pressure produces activated gas or active species which are then used for surface treatment of a substrate. When the discharge gas contains oxygen, for example, surface treatment forms a metal oxide film on a metal circuit on a substrate. If, however, the gas contains hydrogen or an organic substance, a metal oxide film, such as a transparent electrode formed on the surface of a liquid crystal panel, is reduced. Alternatively, by causing discharge to take place adjacent to the surface of a liquid, or bubbled through a liquid, a liquid may be used for surface treatment of a substrate without risk of thermal or electrical damage to the substrate.