A study about the piezoresistive Micro-Electro-Mechanical Systems (MEMS) cantilever for a chemical sensitive - mass based sensor has been carried out to enhance sensor sensitivity. The sensitive region attracts the CO2 molecules there by introducing the stress concentration region (SCR). Three types of SCR geometry designs were first analysed using Intellisuite software to study the effect of stress and its distribution when varying mass is applied at the SCR. The results showed that the rectangular SCR design has the highest stress. Then, the length of rectangular SCR is varied to study the stress distribution along the cantilever. The piezoresistive element was then placed at various positions to obtain the highest stress resulting due to the deflection of the cantilever. The impact due the SCR was also analysed. The testing results of this piezoresistive MEMS cantilever with rectangular SCR had successfully enhanced sensitivity times as compared to the piezoresistive MEMS cantilever without SCR when varying mass is applied. Therefore this SCR approach appears to be suitable for enhancing the sensitivity of a mass-based piezoresistive MEMS cantilever sensor.