A stable sol suspension of Pd-loaded SnO(2) nanocrystals, which is valid for both fundamental studies of semiconductor gas sensor and fabrications of a micro gas sensor, was fabricated by the photochemical deposition of PdCl(4)(2-) onto SnO(2) in an aqueous solution. UV light was irradiated on a mixture of a SnO(2) sol obtained through a hydrothermal treatment of stannic acid gel in the presence of PdCl(4)(2-) and ethanol/water at pH 2. A stable sol suspension of Pd-loaded SnO(2) was successfully obtained by controlling the pH of the above suspension to 10.5 after UV irradiation. Thin-film type sensor devices (film thickness ∼200 nm) using Pd-loaded SnO(2) nanocrystal were successfully fabricated by a spin-coating method. Gas sensing measurements showed that the deposition of Pd on the SnO(2) nanocrystals resulted in large electrical sensitization effect. The maximum gas sensitization effect was obtained at 0.125 mol % Pd loading. Moreover, the Pd loading lowered the temperature, in which the maximum sensor response to H(2) was obtained, due to the efficient catalytic combustion of H(2) on Pd.