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Palladium (Pd) has been widely employed for conventional hydrogen sensors due to the catalytic nature. Pd has been incorporated also with carbon nanotube (CNT) gas sensors for hydrogen sensing. In this study, a liquid-phase electrochemical reaction was proposed to realize a simple and inexpensive fabrication method of a Pd-functionalized CNT hydrogen sensor. The single-walled CNTs were trapped onto a microelectrode under positive dielectrophoresis. The CNT-retaining microelectrode was immersed in a palladium acetate solution together with a graphite rod. DC voltage was applied between the microelectrode (cathode) and the graphite rod (anode) so that palladium acetate could be reduced and catalytic Pd could be electrodeposited on the CNT surface. The CNT sensor could reversibly respond to hydrogen gas in the air in the range of 0.01 % -1 % concentration at room temperature. It was also demonstrated that the Pd-functionalized CNT gas sensor could be fabricated just by dipping the CNT-retaining microelectrode into an aqueous Pd salt solution without applying DC voltage (electroless redox reaction).