A 850nm monolithically integrated optical receiver front end,which consisted of a PIN photodiode and a Transimpedance Amplifier (TIA),was designed and fabricated in a 0.5μm gate-length GaAs PHEMT standard process. A photodiode model was established based on published literature and SILVACO software. The results of experiment show that the matching between model and data of test is good. The eye diagrams of optical receiver are measured at bit rate up to 5 Gb/s. The photodiode has a diameter of 50 μm,a capacitance of 0.51 pF and a maximum dark current of 30 nA. The TIA achieves a -3 dB bandwidth of nearly 10 GHz,a transimpedance gain of 43 dBΩ and minimal equivalent input noise current density of 17.6 pA/Hz^1/2.