We propose a single-chip three-dimensional (3D) electric field microsensor with advantages of small size and high integration. Three orthogonal sensing axes are placed in one chip, in which one sensing element is set in the middle to detect the Z-axis electrostatic field component, and two pairs of sensing elements are designed into the same structure and cross-like arranged to measure X-axis and Y-axis electrostatic field components. In-plane rotary mechanism and strip-type electrodes are adopted in the design. This microsensor is fabricated in a MetalMUMPS process. Experimental results show that the proposed microsensor has linearity errors within 5.5% and electrostatic field measurement errors less than 14.0% in the range of 0~50kV/m.