The effective carrier capture time, which limits the maximum modulation bandwidth of low‐dimensional semiconductor lasers, can be determined by a simple technique as shown in this letter. For demonstration, the technique is applied to InGaAs/InGaAsP multi‐quantum well, InGaAs/GaAs single quantum well and InGaAs/InGaAsP wire lasers, respectively, at low temperature (2 K). Moreover, by comparing quantum‐well lasers with wire lasers, which have different packing densities of the active regions but approximately the same carrier diffusion length before capture, we found that the effective carrier capture times for these two laser types are quite different. This shows the significant role of the scale‐up factor in the contribution of quantum capture time to the total effective carrier capture time, as discussed by S. C. Kan et al. [Appl. Phys. Lett. 62, 2307 (1993)]. © 1996 American Institute of Physics.