The signal value of the transistor-like detector on applied voltage was investigated. It was measure induced-current recording from fluxes of X-ray and optical quanta. A superlinear rise in the resulting signal was observed with increasing voltage. The signal was amplified by a factor of several tens with respect to the value chosen for normalization. A description in terms of the phototriode model gives acceptable values for the main parameters: base width, diffusion length of electrons, and space charge region of the collector. It is important that SiC films with the thickness d similar to 10 mum can be used to detect penetrating radiation, for example, X-ray. The effective thickness of the films exceeds d by the signal amplification factor (and proves to be in range of hundred mum).