Photogating and electrical gating are key physical mechanisms in organic phototransistors (OPTs). However, most OPTs are based on thick and polycrystalline films, which leads to substantially low efficiency of both photogating and electrical gating and thus reduced photoresponse. Herein, high-performance OPTs based on few-layered organic single-crystalline heterojunctions are proposed and the obstacle of thick and polycrystalline films for photodetection is overcome. Because of the molecular scale thickness of the type I organic single-crystalline heterojunctions in OPTs, both photogating and electrical gating are highly efficient. By synergy of efficient photogating and electrical gating, key figures of merit of OPTs reach the highest among those based on planar heterojunctions so far as we know. The production of few-layered organic single-crystalline heterojunctions will provide a new type of advanced materials for various applications.