Organic semiconductors (OSCs) have attracted much attention for low-cost, flexible and human-friendly optoelectronics. However, achieving a high current density to realize an gain narrowing in organic semiconductors by electrically pumping is one of the remaining challenges in the past three decades. Recently we have introduced the novel electrode design for field-effect transistors of single crystal organic semiconductors (sc-OSCs) as an active layer (T.Kanagasekaran et al., Nature Commnications 8, 999, 2017). Equivalent high field-effect mobilities of holes (22 cm2V–1s–1) and electrons (5.0 cm2V–1s–1) were observed in a rubrene single crystal, which are the highest among field-effect transistors so far proposed. Based on our previous achievement, here we report the light emission intensity with relately high current density. For the initial confirmation, we examine the gain medium emission performance by optical pumping, then similarly we have examined by electrical pumping. As the input fluence (F) of a N2 pulse laser (337.1nm) increases, the emission peak intensity of the gain medium greatly increased above the threshold input fluence of Fth of c.a. 10-40 μJ cm–2. At the same time, the FWHM reduced above the Fth. Gain narrowing can be realized when a condition is fulfilled that gain overcomes the loss inside a gain medium. To confirm the gain narrowing, the following two experimental evidences were confirmed by optical pumping. (1) A clear threshold of the output emission intensity (Iout) v.s. laser input power, (2) Significant spectral narrowing in the emission spectrum.