In this study, we aim to develop OSCFF, a force field compatible with GAFF2, specifically designed for organic semiconductors (OSCs). We create an extensive set of approximately 472,000 conjugated molecules by coupling various molecular fragments. These fragments originate from cutting the C-C single bonds of conjugated molecules collected from hundreds of publications within the field of organic electronics. Thus, our bottom-up assembly approach allows for rich diversity in the sample space. Based on these molecules, we construct two molecular datasets: the first consists of around 56,000 fragment geometries with torsion profiles that encompass missing proper dihedral parameters in GAFF2; the second dataset comprises roughly 472,000 optimized molecular geometries with RESP charges. We refine proper dihedral parameters against the torsion dataset to extend GAFF2's parameter library, improving its applicability to conjugated molecules. Additionally, the state-of-the art E3NN model 41 is employed to build the relationship between molecular geometries and RESP charges. The remaining rigid bonded terms are derived directly from the Hessian matrix at GFN2-xTB level. This decision is informed by their limited impact on molecular dynamics (MD) simulations. Meanwhile, if GAFF2 fails to assign an atom type, the non-bonded Lennard-Jones parameters are sourced from the UFF. The high accuracy of OSCFF is demonstrated by comparing OSCFF with quantum mechanical (QM) calculations for dihedral scan results and RESP charges. Furthermore, we also display the agreement of the center of mass (COM) radial distribution function (RDF) obtained from MD simulations using the GAFF2 and OSCFF. Through these developments, we obtain a robust and general force field for OSCs, thus significantly reducing the manual effort required for generating force fields before MD simulations. This, in turn, lays out the foundation for the computational design of OSCs.