Infrared photodetection based on hot electrons is drawing increasing interest due to the capabilities of below-bandgap detection, high tunability of working wavelength, compact size, and room-temperature operation. However, conventional hot-electron photodetectors are mostly based on surface plasmons with a strong polarization preference. In this Letter, we propose a multilayer grating double-junction hot-electron photodetector by introducing an ultrathin Au layer sandwiched between two Au-Si-Au cavities. The multilayer grating system allows the excitation of the guided-mode resonance that shows a weak reliance on the incident polarization and, therefore, realizes the polarization-insensitive optical absorption up to 98%. The special multilayer design facilitates hot-electron generation in the ultrathin Au layers with high carrier transport efficiency, as well as enabling the formation of a double Schottky junction, which doubles the carrier emission probability. The optical and electrical benefits ensure a polarization-independent photoresponsivity ∼1 mA/W at the wavelength of 1470 nm.