Microwave spectra of Ar-28 SiH 4 , Ar-29 SiH 4 , Ar-30 SiH 4 , and Ar-28 SiD 4 were recorded using a pulsed molecular beam Fourier transform microwave spectrometer. The K ϭ 0 and K ϭ 1 components of the J ϭ 3 4 2 through the J ϭ 7 4 6 transitions were measured and assigned in the 9 -24 GHz region. For the primary 28 Si isotopic species, Ar-28 SiH 4 and Ar-28 SiD 4 , a K ϭ 0, A symmetry, a K ϭ 0, F symmetry, a doubly degenerate K ϭ 1, E symmetry, and an l/K-doubled, K ϭ 1, F symmetry rotational progression are observed at the Ϸ1 K rotational temperature of the supersonic expansion. The rotational constants for the K ϭ 0, A state for Ar-28 SiH 4 and Ar-28 SiD 4 are B ϭ 1700.40624(9) MHz and 1630.687073( 22) MHz and the centrifugal distortion constants are D J ϭ 29.089(3) and 20.0198(8) kHz and H J ϭ Ϫ1.91(3) and Ϫ0.851(8) Hz, respectively, where type A expanded uncertainties with a coverage factor, k ϭ 3, are given here and elsewhere. The values of the rotational constants for the K ϭ 0, A, and F states and for the K ϭ 1, E state are in good agreement with the infrared-determined values for Ar-28 SiH 4 . The measured linear Stark effect of the E-state transitions was analyzed to give a dipole moment of 9.24(8) ϫ 10 Ϫ32 C ⅐ m [0.0277(2) D].