The effective minority‐carrier lifetime in the active region of Pb0.86Sn0.14Te/PbTe double‐heterostructure (DH) laser diodes has been experimentally determined for a series of diodes with active‐region widths ranging from 0.7 to 3.9 &mgr;m using a measurement technique which involves observing the dependence of the threshold current density on the duration of a current pulse input. From the data, it is inferred that the interface recombination velocity at the heterojunctions is as high as 1×105cm/sec at 5 °K, while the bulk minority‐carrier lifetime is 4.3 nsec. For a typical double‐heterostructure laser with a 2‐&mgr;m active‐region width, this implies a reduction in the internal quantum efficiency due to interface recombination of as much as 80%.