As a semiconductor with indirect band gap,the light-absorption coeff icient of silicon is a little low,which limits the quantum efficiency of silicon based op toelectronic devices.Inverted pyramidal structure has been proved to be an effective light- trapping structure that can enhance the light absorption of silicon wafer close to Yablon ovitch limit. In this work,random inverted pyramidal structures were fabricated on mono-crys talline silicon wafer by metal catalyzed etching technology,and integrated into PIN phot o-detector to lower the reflectivity of PIN detector.The optical and electrical properties of PIN photo- detector are characterized.The results show that the size of those in verted pyramids ranges from 1μm～3μm,and the weighted average reflectivity of PIN photo-de tector is decreased significantly from 20.18% to 4.77%.The leakage current of the photo- detector is measured to only 0.9nA at room temperature.Furthermore,by adopting the random inverted pyramidal structure into the PIN photo-detector,the spectral response of 0.64A/W is achieved,which is improved by about 33% compared with that of conventional silic on detector. The experimental results demonstrate that the random inverted pyramidal structu re prepared by metal catalyzed etching technology is beneficial to decrease the surface ref lectance and finally improve the spectral response of PIN photodetectors.