We present an insulator-semiconductor-metal plasmonic hot-electron photodetector based on a grating structure that uses monolayer MoS₂ as a semiconductor. Within the MoS₂ bandgap wavelength, the choice of design can be used to increase the photocurrent via the enhanced electric field of surface plasmons. Beyond the bandgap, hot electrons generated by surface plasmons can contribute to the photocurrent, which overcomes the limitation of the semiconductor's bandgap. Using a finite element method simulation, we determined the optimal geometric configuration for the grating and metal parameters. Moreover, we compared our conformal structure with typical planar and metal gratings. The results show that our structure enables the maximum optical enhancement for the semiconductor and the highest utilization ratio of hot electrons among these three architectures. In contrast with a conventional metal-semiconductor-metal structure in which the net current is the difference between forward and backward currents, the proposed structure has only one layer of metal with unidirectional current, which can further enhance the net current and hence the responsivity.