A proposed silicon X-ray photon sensor was irradiated with 60 keV hard γ-rays used in photon-counting computed tomography (CT) scanners, and the response signal was obtained. In this paper, the validity of the response signal was demonstrated by device and circuit simulations. The results indicate that an X-ray photon sensor with a fast response time of 12 ns can be achieved by using an inexpensive silicon material with excellent processability.