A sensor element having a plate-like shape and extending in a longitudinal direction and having a chamfered portion at an edge between a main surface and a rear-end surface or between a main surface and a side surface of the sensor element. The sensor element includes a solid electrolyte layer, an insulating layer disposed on the solid electrolyte layer and constituting at least part of the main surface, and an electrode pad disposed away from the chamfered portion for connection to an outside circuit. Furthermore, the solid electrolyte layer and the insulating layer are exposed at the chamfered portion. Also disclosed are a gas sensor including the sensor element and a method of manufacturing the sensor element.