The Hall Effect sensor is a transducer which converts the magnetic field to an equivalent voltage. Nowadays magnetic sensors based on the Hall Effect have the most widespread usage among different magnetic field sensors. One group of Hall Effect sensor consists of a Hall plate with the circuitries for amplification and converting its output voltage to a suitable output signal for consumers. The Hall plate is a semiconductor plate with two output contacts, showing a differential voltage in the presence of magnetic field. Simplicity, possibility of transforming most of natural signals to magnetic field and feasibility of integration of Hall plate and all corresponding signal conditioning circuits on a single chip in a CMOS technology, has made it a significant component from an economical stand point. They are used in automotive and computer industry, such as disk drives, internal engine ignition timing and antilock braking systems. The Hall sensors generally consist of two main parts, the sensor itself and its processing peripheral circuit. Thus having knowledge about performance of both parts is necessary to increase the performance of the sensor. The sensitivity of Hall plate is limited by its geometrical factor and some non-ideal phenomena such as short circuit effect; on the other hand, noise and offset strongly affect its output voltage accuracy. In this thesis, first the physical parameters of the Hall plate are analyzed and numerical simulation of Hall plate is investigated. Next the design of a low offset amplifier that is appropriate for Hall Effect sensors is studied. Offset and noise limit the performance of many precision electronic systems like sensors and biomedical instruments. Offset originates from any mismatches of different devices that are used in the circuit. Noise can be ltr"