Abstract: An epitaxially grown semiconductor heterostructure has an inner region (5) which is substantially laterally confined by confinement regions (9) and has enhanced transverse confinement by enhanced transverse confinement layers (3, 7). The latter layers are not exposed outside the growth chamber during processing, by stopping the etching for producing the lateral confinement, above the lower enhanced transverse confinement layer (3) and growing such an upper layer (7) after making the lateral confinement regions (9). The structure is intended to be used in particular having the inner region act as an active laser region, for instance in InP-based 1.3 .mu.m wavelength lasers. Then the simultaneous lateral confinement, enhanced transverse confinement and exposure protection enables simultaneously a low threshold current, a small temperature sensitivity and reliable, long life operation. The enhanced transverse confinement layers (3, 7) could comprise aluminium protected from oxidation during processing.