Two techniques of approximating the transient response of a double‐heterojunction light‐emitting diode or diode laser in which there is a nonzero recombination velocity at the heterojunctions are compared to the results of a recently published exact series solution for the transient behavior of such structures. It is shown that both approximations can lead to large quantitative errors—one overestimating and the other underestimating the speed of response—when the active region is wide and the interface recombination is large, but that both approximations are useful and yield similar results when the active region is narrow and interface recombination is small. For devices with narrow active regions and small recombination velocities, it is shown that the transient response can be represented as a single exponential with a characteristic lifetime given by &tgr;[1+(Sv1+Sv2)/D]−1, whereSviandDare the normalized interface recombination velocities and active region width, respectively.