Breakdown voltages of InP/InGaAs avalanche photodiodes have been analyzed with structure parameters, such as multiplication layer width (MLW) and absorption layer thickness. It is shown that there exists a critical MLW,w0, where the breakdown voltage is the lowest. As MLW increases, the breakdown voltage increases slowly in the region of MLW≥w0while the breakdown voltage decreases in the region of MLW≤w0. It is also revealed thatw0is a function of absorption layer thickness. The measured breakdown voltages having MLWs of 0.15–0.4 &mgr;m were reported and compared to the calculated ones, which agreed very well with each other. ©1995 American Institute of Physics.