The pure rotational spectrum of USH and its Li-6 and deuterium isotopomers has been recorded in the region 73-521 GHz using millimeter/sub-millimeter direct absorption techniques. These species were created by the reaction of H2S or D2S and lithium vapor in a dc discharge. Extensive K-a ladder structure was observed for all three isotopomers, indicating that USH is a near-prolate asymmetric top with a (X) over tilde (1)A(1) electronic state. Rotational parameters have been determined for the three species, enabling the calculation of a r(m)((1)) structure. The Li-S-H bond angle was found to be 93degrees, indicating a high degree of covalent bonding in this molecule. (C) 2002 Elsevier Science B.V. All rights reserved.