A short-channel Si metal-oxide-semiconductor field-effect transistor that exhibited a Josephson supercurrent due to the proximity effect was reported recently. In this paper we point out that the dependence of the critical current of this gated weak link on channel carrier concentration is well described by a model that treats the device as a two-dimensional electron gas contacted by source and drain electrodes that are superconducting due to the proximity effect. The critical current is directly related to the boundary condition for the superconducting order parameter at the superconductor-semiconductor interfaces, which is determined by the probability for tunneling through the interfacial Schottky barriers, in contrast to the case of contacts to normal metals. We use a recent superconducting-field-effect-transistor experiment to demonstrate that theoretical results which have been widely and successfully applied to superconductor normal-metal superconductor weak links are not adequate to treat semiconductor-coupled weak links. © 1990 The American Physical Society.