We report on the epitaxial growth, fabrication, and characterization of a resonant-cavity-enhanced separate-absorption and multiplication avalanche photodiode capable of detecting light at 1.55 mu m. The device is grown by molecular beam epitaxy with In0.53GaxAl0.47-xAs layers lattice matched to InP. This detector has exhibited a peak external quantum efficiency greater than 70%, a gain of 8, and a dark current of only 50 nA at 90% of breakdown for a 100-mu m-diam diode.