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Hydrogen-doped ZnO (ZnO:H) thin films were synthesized on glass substrates by using an RF magnetron sputtering system and adding H2 to Ar sputtering gas. The doping effects of hydrogen on ZnO thin films were systematically investigated under various deposition conditions. Resistivity decreased with increasing H2 fraction from 0 to 5%. The Hall effect and infrared reflectance measurements showed that the increase in H2 fraction induced increases in hydrogen incorporation amount and carrier density. These results can be understood by considering that hydrogen acts as a donor, as was previously reported. Effective hydrogen doping in ZnO during synthesis was realized by the suppression of the increase in substrate temperature not only in the bulk but also at the top surface. The lowest resistivity of 1.5 × 10−3 Ω·cm and the highest carrier density of 2.7 × 1020 cm−3 were obtained under optimized conditions without metal dope. [ABSTRACT FROM AUTHOR]