In this paper, we report enhanced performance of quantum dot infrared photodetector (QDIP) by means of surface plasmonic structure. A 10-layer InGaAs quantum dot (QD) structure with AlGaAs barriers were grown on GaAs(001) substrate by molecular beam epitaxy. A periodic gold pillar array was fabricated on the surface of the wafer by i-line lithography and ICP dry etching. The wafer was processed to form a circular mesa of 300 μm diameter. The pillar pitch was varied from 2.0 to 2.5 μm and the pillar diameter was varied from 1.1 to 1.6 μm. The detectors were illuminated from substrate side to evaluate spectral responsivity and detectivity D* at temperature T = 78 K. The pillar array was found to enhance the detector performance at particular wavelength which depends on the pillar property. We found the optimal property of the pillar array whose enhancement peak matches the QDIP's response peak at 7.7 μm. At that wavelength, the responsivity and detectivity were almost doubled compared to the detector without the pillar array.