The postbuckling yield behavior of simply supported rectangular stainless steel plates under combined action of uniform thermal load and uniaxial edge compression are investigated. The nonlinear postbuckling analysis is performed by the finite element method based on the first order shear deformable plate theory with the use of von Karman type nonlinear strains. Yielding of plates at thermomechanical postbuckling load range is predicted by von Mises yield criterion. Several numerical examples for plates with various width-to-thickness and aspect ratios are considered. The yield space is defined by normalized axial compression and temperature change. The yield curves that indicate the load carrying capability of plates without yielding are obtained in the yield space defined. From numerical examples considered, it is found that the shapes of yield curves for the plates with the same aspect ratios are very similar between them regardless of the width-to-thickness ratios of plates. It is also observed that slopes of the yield curves are less steeper as the plate aspect ratio increases, implying that a plate with high aspect ratio has greater thermal, buckling strength compared with the postbuckling strength under compressive load.