Rotational spectra for 3 silicon isotopologues (Si-28, Si-29, Si-30) of cyclopropylmethylsilane (c-C3H5SiH2CH3) have been observed in natural abundance using Fourier-transform microwave spectroscopy, and the dipole moment of the most abundant (Si-28) isotopologue has been determined using the Stark effect. The observed rotational constants (A = 8800.5997(9) MHz; B = 2238.6011(3) MHz; C = 2001.0579(3) MHz) and dipole moment components (mu(a) = 0.195(2) D, mu(b) = 0.674(11) D, mu(c) = 0.362(19) D,mu(total) = 0.790(13) D) for the Si-28 species are consistent with ab initio predictions (MP2/6-311+G(d)) for a gauche conformation about the Si-cyclopropyl bond. All of the observed transitions were split into doublets due to internal rotation of the methyl group. allowing a determination of the V-3 barrier to internal rotation of 6.671(9) kJ mol(-1) for the most abundant isotopologue. This barrier will be compared to those for other Si-CH3 containing COMPOLInds and will be related to a partial structure determination from the available microwave and ab initio data.