Organic semiconductor materials exhibit promising prospects for flexible device applications due to their excellent solution processability and superior charge transport performance. This work proposed a method for preparing a stretchable organic semiconductor material. By using benzophenone as a photoinitiator, the conjugated polymer 3,6-dithiophene-2-yl-2,5-dihydropyrrolo [3,4-c] pyrrole-1,4-diketone (4Si) was crosslinked with polydimethylsiloxane. The alterations in the electrical and mechanical properties of the polymer films were thoroughly investigated on both pre- and post-crosslinking. Compared to the uncrosslinked 4Si and blend films, the electrical properties of the crosslinked films slightly decreased, while the mechanical properties were enhanced. The crack onset-strain has increased from 30% to 50%. Furthermore, at 100% strain, the crosslinked film exhibited a mobility of 0.36 cm²·V^-1·s^-1 in the parallel strain direction, which is 1.44 times higher than the initial mobility.