The fundamental trade‐off between high intrinsic carrier mobility and solution processability severely limits the development of organic single crystals (OSCs). For instance, while 2,6‐diphenylanthracene (DPA) is a benchmark candidate for direct X‐ray detection, its intrinsic insolubility hinders solution processing, and conventional solubilizing alkyl modifications inevitably degrade transport efficiency. Here, we report a facile surfactant‐assisted near‐room‐temperature solution epitaxy method to overcome this bottleneck, fabricating centimeter‐scale ultrathin DPA two‐dimensional (2D) OSCs utilizing a common solvent at 35℃. Electrical characterization reveals that the as‐fabricated DPA 2DOSCs exhibit a maximum mobility of 5.55 cm²/(V ∙ s), an order of magnitude higher than that of the alkylated C₆‐DPA counterpart. This superior charge transport efficiency directly translates into exceptional X‐ray detection performance, achieving a high sensitivity of 7.02 × 10³ μC/(Gy∙cm²) and a low detection limit of 24.05 nGy/s. This work not only provides a facile low‐energy route to process intrinsically insoluble organic semiconductors but also establishes high‐mobility DPA 2DOSCs as a premier platform for next‐generation large‐area organic direct X‐ray detectors.