Carbon nanotubes (CNT) have been studied intensively for explorations of their unique electrical and mechanic properties in many applications. However, direct and functional integration of carbon nanotubes with silicon to form an electronically functional structure or device has remained a great challenge. Whereas vertically aligned bundles of nanotubes have been grown previously on silicon, the integration is mechanical, rather than electronical, in nature and the application of such mechanical integration is rather limited. In this work, we report on electronically functional integration of carbon nanotube with silicon, i.e., the formation of an electronic heterojunction by controlled growth of vertical and highly ordered array of ‘carbon nanotube - silicon’ (CNTS) heterojunctions of uniform diameter, length, and alignment. Moreover, we examine it as a hyperspectral photodiode. From the measured spectral dependence of the photocurrent, one may also extract the band gap of the nanotubes, which we find to be in agreement with that determined from conductance measurements. Mechanism of the infrared photocurrent response is elucidated by the current-voltage (I-V) and radiation intensity-photoresponse measurements. The linear intensity dependence of the photoresponse in the absorption ranges of Silicon and CNTs and the measured I-V characteristics all suggest that the photocurrent responses corresponding to the Silicon and CNT bands both originate from the intrinsic functionality of the heterojunction.