a sensor or actuator structure having a first part and at least one second part . the second part is mobile and electrically insulated in relation to the first part . the first and second parts are formed in a noninsulating substrate wafer and have mutually adjacent edges separated by at least one cut which goes right through the substrate . the second part has at least one extension in the form of a beam which has one end fixed onto the first part by way of an electrically insulating joint . this device may be used in an accelerometer .