A mesh patterned n-type single-crystalline silicon nanomembrane (SiNM) created from a silicon-on-insulator (SOI) wafer is complementally combined with a p-type pentacene layer to form a heterogeneous p-n junction on a flexible plastic substrate. Excellent rectifying characteristics are obtained from the heterogeneous p-n diode. The diode also exhibits photosensitivity at visible wavelengths with a photo-to-dark current ratio exceeding four orders, a responsivity of 0.7 A/W, and an external quantum efficiency of 21.9% at 633 nm. Over 60% average transmittance in the visible spectrum is measured from the heterogeneous multilayer junction on a plastic substrate. Outstanding mechanical bending characteristics are observed with up to 1.08% of strain applied to the diode. These results suggest that organic-inorganic heterogeneous integration may be a viable strategy to build flexible organic-inorganic heterojunction devices and thus enable a number of novel multifunctional applications.