This paper reports on the development and characterization of novel in-plane CMOS-based stress sensors featuring equal sensitivities towards the two mechanical shear stress components sigma_xy = (sigma_x'x' - sigma_y'y') / 2 and sigma_x'y'. The sensor structures are based on symmetric n-well resistors with eight contacts. A geometric parameter variation is performed using FEM simulations to adjust the stress sensitivities of different sensor layouts. For characterization, in addition to a four-point bending bridge used to exert normal stresses (sigma_x'x' - sigma_y'y'), a novel torsional bridge setup was developed to apply well-defined shear stress sigma_x'y' to the surface of silicon beams diced parallel to the <110> crystal direction of silicon and containing the stress sensor elements. The measured sensitivities are consistent with simulated values.