This paper discusses the design of a sensitive micromachined electric field sensor. The sensor operation is based on chopping an incident electric field using a perforated shutter and then differentially measuring the induced charge on two sets of electrodes which are situated under the shutter. To lower the required actuation signal levels, thermal actuators are used to bring and keep the structure under resonance. The produced displacements are mechanically amplified to allow for relatively large displacements with small actuation signals. Simulation and experimental results are also presented. Fabricated devices have a linear response and are capable of measuring fields as small as 42 V/m.