Surface-modified organic semiconductors and methods for making surface-modified organic semiconductors are disclosed. More particularly, surface-modified thin films are provided, the surface-modified thin films comprising a first layer comprising a polyaromatic organic semiconductor and a surface layer in direct contact with the first layer, the surface layer comprising an addition reaction product of the polyaromatic organic semiconductor with, for example, a dienophile, wherein the first layer is substantially free of the addition reaction product of the organic semiconductor with the dienophile. Also provided are surface-modified single crystals comprising a core comprising a polyaromatic organic semiconductor and a coating in direct contact with the core, the coating comprising, for example, an addition reaction product of the polyaromatic organic semiconductor with a dienophile, wherein the core is substantially free of the addition reaction product of the organic semiconductor with the dienophile.