Stress is the main parameter for monitoring the health infrastructures of bridges, railroads, and skyscrapers in the Structural Health Monitoring Systems (SHMS). The strain gauge device is utilized to measure the stress generated by a tension load applied on an object material and then converts the stress into an electrical output (i.e. resistance). Micro-electro-mechanical systems (MEMS) strain gauge is mainly used for advanced applications due to high sensitivity, small size, and low power consumption. To estimate stress, the piezoresistive effect was typically used for stress or strain measurement. Then, the strain gauge is made of a thin layer of metals, alloys, or semiconductor materials. To improve the performance of MEMS strain gauges, some structures of silicon (i.e. thin monofilament, a thin membrane, and surface groves or trench) have been introduced. However, a new structure of a silicon micro-beam is not considered yet. In this study, a silicon micro-beam of MEMS piezoresistive is used to amplify the stress on a steel bar in one direction. A high gauge factor of strain gauge can be obtained from 130 to 270 in a wide range of dimensions of micro-beam. The obtained results can be applied to design higher sensitivity of MEMS piezoresistive strain gauge based on micro-beam structure to detect the stress on a steel bar object in a one direction.