MSM(Mental-Semiconductor-Mental)photodetector has been widely used for its low capacitance and high bandwidth.For example,it can be used for space communication,remote sense and so on.But the development of MSM devices is still hindered by the dark current.In this paper,the 100×100 μm2 InGaAs-MSM photodetector is successfully fabricated.The dark current density is reduced to 0.6 pA/μm2(5 V)by designing InAlGaAs/InGaAs short period superlattices and InAlAs Schottky barrier enhancement and this improves the SNR.Parameters of the device are characterized as follows:the 3dB bandwidth is 6.8 GHz,the rise time is 58.8 ps,the responsibility is 0.55 A/W at 1550 nm and the external quantum efficiency of the absorption region is 88%.Inhibition mechanisms of the short period superlattices and Schottky barrier enhancement are analyzed.