Surface plasmon waves and Rayleigh anomaly are characteristic optical phenomena exhibited by periodic subwavelength grating structures. In this paper, a hybrid metal-dielectric metasurface is proposed to improve the photoresponse of Ge/Si quantum dot infrared photodetectors (QDIPs) with limited absorption layer thickness. The composite metasurface consists of a regular array of silicon pillars. The pillars protrude through subwavelength holes in a perforated gold film on the detector top. We demonstrate that by combining effects of dielectric and plasmonic metal components, the QDIP photoresponse can be significantly improved compared to case when all-dielectric and metal gratings work alone. We observe about four times photoresponse enhancement with the hybrid metasurface device relative to a common plasmonic design with a two-dimensional metal hole array. Compared with a bare QDIP, the peak responsivity of the hybrid detector at a wavelength of 4.4 µm is increased by a factor of 15. The enhanced sensitivity is supposed to arise from coupling of the surface plasmon resonance and diffractive effect related to the Rayleigh anomaly.