Microwave spectra of Ar–28SiH4, Ar–29SiH4, Ar–30SiH4, and Ar–28SiD4 were recorded using a pulsed molecular beam Fourier transform microwave spectrometer. The K = 0 and K = 1 components of the J = 3 ← 2 through the J = 7 ← 6 transitions were measured and assigned in the 9–24 GHz region. For the primary 28Si isotopic species, Ar–28SiH4 and Ar–28SiD4, a K = 0, A symmetry, a K = 0, F symmetry, a doubly degenerate K = 1, E symmetry, and an l/K-doubled, K = 1, F symmetry rotational progression are observed at the ≈1 K rotational temperature of the supersonic expansion. The rotational constants for the K = 0, A state for Ar–28SiH4 and Ar–28SiD4 are B = 1700.40624(9) MHz and 1630.687073(22) MHz and the centrifugal distortion constants are DJ = 29.089(3) and 20.0198(8) kHz and HJ = −1.91(3) and −0.851(8) Hz, respectively, where type A expanded uncertainties with a coverage factor, k = 3, are given here and elsewhere. The values of the rotational constants for the K = 0, A, and F states and for the K = 1, E state are in good agreement with the infrared-determined values for Ar–28SiH4. The measured linear Stark effect of the E-state transitions was analyzed to give a dipole moment of 9.24(8) × 10−32 C · m [0.0277(2) D].