Quantum well infrared photodetectors (QWIPs) have demonstrated applications in many different areas, such as medical and biological imaging, environmental and chemical monitoring, and infrared imaging for space and night vision. However, QWIPs still suffer from low quantum efficiency and detectivity compared with mercury cadmium telluride (MCT) based interband photodetectors, which dominate current infrared detector market. Besides, n-type QWIPs cannot detect the normal incident infrared radiations because of the polarization selection rules of intersubband transitions. Here, we used periodic holes array perforated in gold film to convert normal-incident infrared light to surface plasmon waves, which can excite the intersubband transitions and be absorbed by quantum wells (QWs). Our 3D FDTD simulation results show that electric field component in the QWs growth direction can be enhanced by more than 5 times compared with the total electric field intensity without any plasmonic arrays. The experimental results show that the photodetector has a peak detection wavelength at ∼8 μm with a high detectivity of ∼7.4×1010 Jones, and the photocurrent spectrum was very close to the simulation result of the electric field enhancement spectrum.