In order to achieve a very high electron density in Si δ-doped GaAs grown by metal organic vapour-phase epitaxy (MOVPE) at 630°C, the effect of growth parameters on the electron density of Si δ-doped GaAs has been investigated. A linear increase of the electron density with the SiH 4 flow rate was observed regardless of the H 2 flow rate (or the gas flow velocity) over the region of 0.5-2 s.1.m. The dependence of the electron density on the H 2 flow rate at the given SiH 4 partial pressure is contrary to the previous reports. In the experimental range of the SiH 4 flow rate, the electron density proportionally increases with an increase in δ-doping time until reaching the saturated value of ∼8 10 1 2 cm - 2 at the δ-doping time of ∼40 s. Taking the previous reports on MOVPE growth of Si δ-doped GaAs into account, the parameters dominating Si δ-doping concentration at different H 2 flow rate regions are discussed. The optimised H 2 flow rate was observed. At the growth temperature of 630°C, we obtained an electron profile of a Si δ-doped layer in GaAs with a peak concentration of 6.1 10 1 8 cm - 3 and a profile width of 55 . The average electron density of the Si δ-doped nini doping superlattice in GaAs is ∼4.8 10 1 8 cm - 3 .