Hall effect magnetic sensors have gradually gained dominance in the market of magnetic sensors during the past decades. The compatibility of Hall sensors with conventional CMOS technologies makes monolithic Hall sensor microsystem possible and economic. An attractive application is the contactless current sensor by using Hall sensors to measure the magnetic field generated by the electrical current. However, Hall sensors exhibit several non-idealities, i.e., offset, noise and sensitivity drift, which limit their precision. Therefore, effective techniques to reduce these imperfections are desired. This thesis presents the design of a new readout scheme for Hall magnetic sensor with low offset, low noise and low sensitivity drift. The Hall sensor is realized in N-well as Hall plate and modeled in Verilog-A for the purpose of co-simulation with interface circuits. The self-calibrated system is composed of two identical Hall plates, preamplifiers and a first-order ΣΔ modulator, which can be fully integrated monolithically. Four-phase spinning current technique and chopper stabilization technique have been employed to reduce the offset and 1/fnoise of Hall platesand OTA, respectively. Integrated coils are used to generate the reference magnetic field for calibration. The preamplifiers amplify the signal and separate the Hall voltage and reference voltage. The ΣΔ modulator reduces the thermal drift by using Hall voltage as the modulator input and reference voltage as the DAC output. This new calibration technique also compensates the thermal drifts of the biasing current and readout circuits. The overall system is implemented in NXP140nm CMOS process with 1.8V supply. The Virtuoso/Spectre simulation results show residual drifts lower than 10ppm/ ̊C, which are 3-5 times lower than the state of the art. The input magnetic field and temperature range are ±100mT and -40 ̊C to 120 ̊C, respectively.