HAMAMATSU realized MSM (Metal-Semiconductor-Metal) Photodetectors having ultrafast responses. The GaAs MSM Photodetector G4176 features 30ps response time for both rise & fall while keeping a low dark current (100pA at Ta=25 ｰC). The rise time of the InGaAs MSM Photodetector G7096 is 40ps. Symmetrical and interdigital Schottky contacts are fabricated at the sensitive area, whose size can be larger than other kinds of fast response photodetectors. This makes easier to set up with optics. Therefore, MSM Photodetectors are suited for measurements of optical high-speed waveform and optical communications.