The invention provides a method of forming an electric field gap device, such as a lateral field emission ESD protection structure, in which a cathode layer is formed between dielectric layers. Anode channels are formed and they are lined with a sacrificial dielectric layer. Conductive anode pillars are formed in the anode channels, and then the sacrificial dielectric layer is etched away in the vicinity of the anode pillars. The etching leaves a suspended portion of the cathode layer which defines a lateral gap to an adjacent anode pillar. This portion has a sharp end face defined by the corners of the cathode layer and the lateral gap can be defined accurately as it corresponds to the thickness of the sacrificial dielectric layer.