We report detections of six high-redshift (1.8 ≤ z ≤ 6.4), optically luminous, radio-quiet quasars at 350 μm, using the SHARC II bolometer camera at the Caltech Submillimeter Observatory. Our observations double the number of high-redshift quasars for which 350 μm photometry is available. By combining the 350 μm measurements with observations at other submillimeter/millimeter wavelengths, for each source we have determined the temperature of the emitting dust (ranging from 40 to 60 K) and the far-infrared luminosity [(0.6-2.2) × 10^(13) L⊙]. The combined mean spectral energy distribution of all high-redshift quasars with two or more rest-frame far-infrared photometric measurements is best fit with a graybody with temperature of 47 ± 3 K and a dust emissivity power-law spectral index of β = 1.6 ± 0.1. This warm dust component is a good tracer of the starburst activity of the quasar host galaxy. The ratio of the far-infrared to radio luminosities of infrared-luminous, radio-quiet high-redshift quasars is consistent with that found for local star-forming galaxies.