Highly conductive films of zinc oxide have been prepared by reactive rf magnetron sputtering from an oxide target. Film conductivities ranging from ∼10−8&OHgr;−1 cm−1to 5×102&OHgr;−1 cm−1can be obtained depending on the sputter conditions. Films with sheet resistivities of 85 &OHgr;/&laplac; showed little absorption and ∼90% transmission between &lgr; = 4000→8000 A˚. A second low power discharge at the substrate is used to initiate growth of the highly conducting material on room‐temperature substrates. Thus, during the deposition of insultating ZnO, turning on this second discharge causes the deposition to ’’switch’’ from low conductivity to high conductivity material. This is of particular interest in the fabrication of semiconductor‐insulator‐semiconductor solar cells where precise control over the thickness of the insulating layer is necessary and where a highly transparent and conductive window‐junction layer is required.