δ doping is demonstrated to be a scheme for reducing carrier profile width and increasing doping density. We have grown multilayers of planar Si doped GaAs by molecular-beam epitaxy and profiled the dopant distribution by electrochemical C–V profiling and secondary ion mass spectroscopy. It is estimated that the delta doping could be confined to approximately three atomic layers. The measured profiles appear much broader due to instrumentational broadening. Secondary ion mass spectroscopy profiles measure a full width at half-maximum (FWHM) of 6.3 nm for Si in GaAs, while C–V profiles measure FWHM of 3.1 nm.