In the current investigation, the piezoresistive effect in a van der Pauw (VDP) stress sensor subjected to biaxial stress was considered. The VDP resistance equations were combined with the silicon piezoresistivity equations to yield relations for the change in resistance of a VDP sensor in terms of the applied state of stress. Then the sensitivity of the VDP sensor to biaxial stress was determined analytically and simulated numerically. The biaxial stress states considered were those for a circular diaphragm under pressure. The numerical calculations involved the use of anisotropic conduction based simulations, implemented in MATLAB using the finite difference technique. The VDP sensitivities to biaxial stress were compared to the sensitivity for the conventional piezoresistive stress sensor. It is observed that the theoretical (based on analytical and numerical results)pressure sensitivity of the new VDP sensor is about three times greater than the conventional counterpart. Analysis was performed for both p-type and n-type Silicon. It is determined that the angle of the VDP sensor with respect to the Silicon crystallographic axes can and should be optimized, depending on Silicon dopant, and the optimum orientation angles are determined. Copyright © 2007 by ASME