High performance GaAlAs/GaAs heterostructure avalanche photodiodes (APD) have been fabricated. The spectral response of these devices are from 0.48 μm to 0.89 μm. The quantum efficiency at unity gain is as high as 95%. Microwave gain (273 MHz) of 42 dB has been observed in these devices. Dark current is extremely low ~ l0 -12 A at half the breakdown voltage. Low noise characteristics of the Read structure APD cannot be verified at this moment because of the poorer performance than the traditional LPE heterostructure APD. With careful design, III-V heterostructure photodiode can have response time as low as 5 ps.