Microbeams have a wide range of applications as sensors and actuators in nanotechnology, biotechnology, microelectromechanical systems, and optics. Given their micrometer dimensions, these beams make precision mass sensors of sub-nanogram accuracy. An important challenge regarding mass sensors is to enhance their sensitivity and accuracy. Considering the fact that, this type of sensor operates based on the resonance frequency variations caused by nanoparticle absorption in the dynamic mode, the geometry of the microbeam is considered an important parameter affecting their sensitivity. This paper studies the rectangular microbeam, which is one of the most commonly used types of mass sensors. Three main models were selected by applying inner and outer cuts on the microbeam, and vibrating simulation was carried out using ABAQUS software for a total of 36 mass sensor configurations with different aspect ratios. Simulation results in two selected rectangular microbeam models with outer cuts show the sensitivity of the microsensor increases with increased microbeam rigidity. The triangular hollow microbeam was found to be the best design among the four models selected to be used as mass sensors.