The photo-response of 3C-SiC pn homojunction photodiodes was measured at high temperature up to 673K. At 473K, the response is hardly different from that at the room temperature. At 573K and 673K, the peak is red shift and lowering comparing that of 298K. The response increases on the long-wavelength region of the profile because of an increase in optical absorption coefficient on increase in temperature. Responsivities at various temperatures were calculated using one-dimensional diffusion model. The calculated profiles of response are qualitatively in agreement with the experimental results except for that of 473K.