Gd-doped ZnO (GZO) films were deposited on glass substrates at various growth temperatures by using radio-frequency (rf) magnetron sputtering. The experimental data showed that the growth temperature had a significant effect on the structural, optical, and electrical properties of the GZO films. The GZO film deposited at 400 °C exhibited a preferential growth orientation along the (002) plane with a thickness of 1480 nm, an average optical transmittance of 86.5% in the visible wavelength range, an optical band gap of 3.18 eV, and an electron concentration of 1.9 × 1020 cm−3, where the highest figure of merit was obtained. The increase in the figure of merit results from the decrease in the electrical resistivity with increasing growth temperature. The optical band gap energy Eg as a function of the growth temperature T, calculated by using the Tauc model and parabolic bands, is expressed as eV. The results suggest that the optimum growth temperature for depositing high-quality GZO films is 400 °C.