If a Darlington transistor is triggered by the photocurrent output from an individual photodiode, the electromagnetic interference (EMI) problem may still exist because the direct input of the Darlington is an actually electronic signal. To eliminate the EMI problem completely, we propose an absolutely light-activated Darlington transistor made of SiC, in which p-SiCGe/n-SiC heterojunction is employed to produce a base current by means of optical illumination. Performance of the novel light-activated power switch was simulated using MEDICI tools, which has shown that the light-activated device has very good switching characteristics especially for a triggering light intensity greater than 0.23 W/cm2. For a relatively weak light, the device can be switched to the ON state only for a higher bias voltage.