This paper presents the development and characterization of a high-Q microcavity electric field sensor (MEFS) using Pound-Drever-Hall (PDH) detection. The MEFS is based on thin-film lithium niobate (TFLN) photonic integrated circuits on a silicon chip. The PDH scheme allows the MEFS to achieve a detection sensitivity of 5.2 μV/(m√Hz), surpassing previous lithium niobate electro-optical sensors by nearly two orders of magnitude and comparable to atom-based quantum sensing approaches. The MEFS also offers a bandwidth up to three orders of magnitude broader than quantum sensing approaches and can measure fast electric field amplitude and phase variations in real-time. The high sensitivity and broad bandwidth of the MEFS make it a significant step towards building electric field sensing networks and expanding the application spectrum of integrated microcavities. The paper discusses the fabrication, packaging, and experimental setup of the MEFS, as well as its performance characterization, including linearity, dynamic range, and real-time measurement capabilities. The authors also explore the potential for further optimization and integration of the MEFS with other components, such as on-chip lasers and photodetectors, to enhance its robustness, size, weight, and power consumption.This paper presents the development and characterization of a high-Q microcavity electric field sensor (MEFS) using Pound-Drever-Hall (PDH) detection. The MEFS is based on thin-film lithium niobate (TFLN) photonic integrated circuits on a silicon chip. The PDH scheme allows the MEFS to achieve a detection sensitivity of 5.2 μV/(m√Hz), surpassing previous lithium niobate electro-optical sensors by nearly two orders of magnitude and comparable to atom-based quantum sensing approaches. The MEFS also offers a bandwidth up to three orders of magnitude broader than quantum sensing approaches and can measure fast electric field amplitude and phase variations in real-time. The high sensitivity and broad bandwidth of the MEFS make it a significant step towards building electric field sensing networks and expanding the application spectrum of integrated microcavities. The paper discusses the fabrication, packaging, and experimental setup of the MEFS, as well as its performance characterization, including linearity, dynamic range, and real-time measurement capabilities. The authors also explore the potential for further optimization and integration of the MEFS with other components, such as on-chip lasers and photodetectors, to enhance its robustness, size, weight, and power consumption.