Microcantilevers are one of the basic micromechanical structures. They are fixed at one ends and the other ends can move freely like a diving board. Their sizes are in the micrometer and nanometer ranges. Microcantilevers are called microcantilever sensors when their surfaces are functionalized to detect specific molecules. Since these sensors have offered remarkable possibilities in detection, they have been used in many fields such as clinical diagnosis, drug screening and pathogen detection. In the microcantilever sensors, various detection methods are available such as piezoresistive, optical, capacitive and piezoelectric. Each sensing method holds own advantages and disadvantages. By the advantage of allowing integration of the read-out electronics on the same chip, piezoresistive detection becomes prominent. So piezoresistive detection is chosen in this work and a basic piezoresistive microcantilever biosensor design is introduced. Furthermore, by making geometrical alterations on microcantilever and piezoresistive layer, effects of these variations upon sensitivity, vertical displacement and change in resistance are investigated. Additionally, effects of different shaped holes upon sensor are studied.