Stability of the Zn doping profile in InGaAs/InGaAsP modulation‐doped multiple quantum well (MD‐MQW) structures grown by low‐pressure metalorganic vapor‐phase epitaxy (MOVPE) has been investigated by secondary ion mass spectrometry and transmission electron microscope with wedge‐shaped samples. Although excellent stability of Zn profile is confirmed in an as‐grown sample with modulation doping (d=3 nm CZn=1×1018 cm-3), the modulation‐doping structure diminishes after the second epitaxial regrowth of a p‐InP layer (CZn=1×1018 cm-3) carried out by either liquid phase epitaxy or MOVPE, which is applicable for buried heterostructure lasers. However, the modulation‐doping profile is successfully preserved even after regrowth of the p‐InP layer for 90 min in a sample constructed of an undoped InP clad layer instead of a p‐InP clad layer superposed on the MD‐MQW layers. A Zn diffusion coefficient in the modulation‐doped region is extremely small, having a value of less than 7×10-18 cm2/s. The maximum Zn concentration in the modulation‐doped region in barrier layers was found to be 2×1018 cm-3 for obtaining a stable modulation‐doping structure. It is proposed that the suppression of both interstitial Zn atoms and subsequently produced interstitial group III atoms, which are generated in the p‐InP clad layer via a kick‐out mechanism and diffuse into the MD‐MQW region, is important for preserving modulation‐doping structure. © 1996 American Institute of Physics.