Our aim has been the development of a new radiation detector made of n-doped Silicon and Multiwall Carbon Nanotubes (CNT). By the deposition of CNT through Chemical Vapor Deposition on the surface of silicon substrate a Si-CNT heterojunction is obtained with peculiar photoconversion characteristics. We studied the photosensitivity parameters of this heterojunction looking for the amplification of the collected photoinduced charge through structured silicon substrates. Results encourage the attempt to use SiPM-like substrates to obtain a new single photon photodetector sensitive in a wide wavelength range from UV to near infrared.