Abstract: Gas source molecular beam epitaxy have been used in the growth of InAlAs/InGaAs MSM-PD structure, in which InAlAs ultra thin layer was used as Schottky barrier enhancement material. High performance MSM-PDs have been const ructed on the grown wafer using optimized growth conditions. High breakdown voltage of ＞30V and low dark current density of 3pA/μm² at 10V bias have been achieved, this is the best result reported. Fast transient response of ＜20ps rise time and ＜40ps FWHM have been measured on this devices. The results confirm the inference that GSMBE is a superior method for the growth of III-V materials with high layer and interfacial quality, especially for InP based InAlAs/In GaAs system.