Abstract.  A broadband perfect light absorption scheme relying on planar layers of lossy metallic and semiconductor films without structure pattering for hot electron photodetection is proposed and demonstrated. The nontrivial reflection phase shift occurring in the ultrathin lossy metal film is responsible for the strong resonance effects of the metal–semiconductor–metal (M-S-M) structures. Broadband and perfect light absorption is demonstrated experimentally for the platinum (Pt)—titanium dioxide (TiO2)—aluminum (Al) absorber, in which the ultrathin (10 nm) Pt layer electrically serves as the hot electron emitter. Under the monochromatic light illumination, the proposed M-S-M diode shows a clear hot-electron-based photoresponse.