Conducting and transparent thin films (60 and 120 nm) of tin oxide were prepared by reactive rf planar magnetron sputtering of an undoped hot‐pressed polycrystalline tin oxide target onto unheated substrates. The effects of the oxygen partial pressure on the room‐temperature electrical properties of the films were studied. The properties vary markedly with, for example, the value of resistivity ranging from a high of ∼8×10−1&OHgr; cm to a minimum value of about 3×10−3&OHgr; cm. This minimum is the lowest value of resistivity reported for undoped films prepared on unheated substrates. These films have optical transmittances greater than 80% averaged between 850 and 550 nm.