This work presents a compact three-dimensional Magnetic Field Sensor (MFS) designed in standard Complementary Metal-Oxide-Semiconductor (CMOS) technology. A circular Vertical Hall Device (VHD) for horizontal magnetic field detection and a split- drain Horizontal Hall Device (HHD) for the vertical magnetic field detection are integrated to implement the three-dimensional M FS. This merged design has the advantage of smaller area and lower power consumption. The sensitivity of the vertical hall device (ring-shaped magneto-resistor) and the horizontal hall device (Split-Drain Magnetic Field-Effect Transistor (SD-MAGFET)) is estimated as 0.11V/T and 2.88V/T respectively. The vertical direction of the magnetic field detection demonstrates a higher sensitivity. A high gain cascode differential amplifier is integrated with the sensor to further amplify the magnetic signal.