Because of the relative large in size, stress measurements on advanced microelectronic packaging through the traditional piezoresistive sensor is not appropriate. Consequently, size-reduced piezoresistive sensors up to 5 μm edge length with a supplementary circuit design is proposed, and parameter extractions were performed through suitable methodologies in this paper. According to the experimental data, it is concluded that a single pair of piezoresistive coefficients can be employed for different size-reduced sensor designs.