Two-dimensional electron systems were realized in InSb quantum wells with AlxIn1-xSb barrier layers delta-doped with Si. Measured electron mobilities in multiple-quantum-well structures were as high as 41000 cm(2)/V s at room temperature and 209000 cm(2)/V s at 77 K. Simple models can be used to explain the observed dependencies of the electron density on the quantum-well-to-dopant distance and on the, number of quantum wells. Characterization by atomic force microscopy indicates that layer morphology may be a factor limiting electron mobility.