Lattice-matched InP/InxGa1<FONT FACE=Symbol>-</FONT> x As short period superlattices (x = 0.53) delta-doped with Si in the middle of the InP barriers were studied. The samples had a high carrier concentration which filled two minibands. In addition to a peak associated with the electrons from the second miniband, E2, the Shubnikov-de Haas spectra showed a well resolved doublet structure that is assigned to E1 electrons of superlattice wave vectors kz = 0 and kz = pi /d. From the lineshape of the Shubnikov-de Haas oscillations, an E1 quantum mobility of 970 cm2/Vs was deduced, which represents an increase of about 40% over the value for periodically delta-doped semiconductors. The photoluminescence ex- hibits a band at photon energies higher than the InGaAs bandgap and whose FWHM approximates the Fermi energy of the confined carriers. Thus the photoluminescence observed is consistent with the recombination of electrons confined by the superlattice potential and photoexcited holes.