GaAs pin-photodiodes (PIN-PD's) with a wide bandgap AlGaInP window layer were demonstrated for a graded-index plastic optical fiber (GI-POF) data link at a wavelength of 650 nm as a high-speed and low-bias operation receiver, High quantum efficiency of over 80% was obtained in the wavelength range from 600 to 850 nn, A 3-dB bandwidth of 4.3 GHz was achieved in 90 mu m phi PIN-PD's. High speed operation up to 600 Mb/s in 210 mu m phi PIN-PD's was demonstrated under the bias free condition.