Gallium-doped zinc oxide (GZO) films were deposited by dc planar magnetron sputtering using a GZO ceramic target. Deposition was carried out under various conditions of substrate temperature (RT-700 degreesC), residual water pressure (1.61 X 10(-4)-2.2 X 10(-3) Pa), and H-2/(Ar+H-2) flow ratio (0-15%). A relatively low resistivity of 5 X 10(-4) Omega cm was obtained for films deposited at 400 degreesC, attributed to an increase in carrier density and Hall mobility. In the case of 100% At gas, the grain size and electrical properties of the GZO films deposited on RT substrates were heavily affected by residual water pressure in the deposition chamber. The resistivity increased from 3.0 X 10(-3) to 3.1 X 10(-2) Omega cm and the grain size of the films decreased from 24 to 3 nm when the residual water pressure was increased from 1.6 X 10(-4) to 2.2 X 10(-3) Pa. However, the introduction of H-2 to decrease the resistivity resulted in a decrease of grain size in proportion to H-2 flow ratio.