The cross‐sectional geometry of Nernst—Ettingshausen generators and refrigerators is optimized for essentially rectangular geometry and also for Norwood's spiral screw thread configuration. The magnetic field, heat flow, and electrical current flow are assumed to be mutually perpendicular. The derivation is carried out without any restrictive assumptions concerning electric current distribution. There are no restrictive assumptions about the temperature dependence of &kgr;, &sgr;, or the Nernst coefficient. The expressions for the boundary of the device are given in parametric form with temperature as the parameter. Formulas are given for use in estimating the effect of incomplete optimization.