We report a new Al0.48In0.52As/Ga0.47In0.53As avalanche photodiode with separate absorption and multiplication regions (SAM APD) and an undoped spacer layer in the gain region. These devices grown by molecular beam epitaxy, have very low dark currents (4 nA at the onset of gain) which compare favorably with state‐of‐the‐art InP/Ga0.47In0.53As SAM APD’s. Avalanche gains ≊60 and a high speed of response with a gain‐bandwidth product ≊10 GHz are demonstrated. Receiver sensitivity measurements at 420 Mb/s and &lgr;=1.3 &mgr;m with a Si bipolar transistor preamplifier yielded −36.0 dBm at a 10−9bit error rate.