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A high optical-gain /spl beta/-SiC phototransistor (PT) with a bulk-barrier structure has been fabricated on a silicon substrate. It demonstrated high optical gains of 145 at 25/spl deg/C and 106 at 250/spl deg/C, under a 10-V bias and 10-μW incident optical power with a wavelength of 500 nm. The high optical gains at elevated temperatures are attributed to not only the excellent high-temperature properties of SiC materials, but also the bulk-barrier structure, in which the formed potential barrier, the short base region and an effect of thinning the quasi-neutral base region to zero thickness lead to a greatly enhanced current gain. The developed /spl beta/-SiC bulk-barrier PT possesses a potential for high-temperature high-gain optical-sensing applications.