Warm dark matter (WDM) may resolve the possible conflict between observed galaxy halos and the halos produced in cold dark matter (CDM) simulations. Here we present an extension of MSSM to include WDM by adding a gauge singlet fermion, \bar{\chi}, with a portal-like coupling to the MSSM Higgs doublets. This model has the property that the dark matter is {\it necessarily warm}. In the case where M_{\bar{\chi}} is mainly due to electroweak symmetry breaking, the \bar{\chi} mass is completely determined by its relic density and the reheating temperature, T_R. For 10^2 GeV