A surface-mountable electrical circuit protection device comprising: a central planar layer forming a first polymeric positive temperature coefficient resistor having first and second major surfaces, a second electrode layer formed at the second major surface and in intimate electrical contact therewith; and first and third terminal electrodes (24, 26), the third terminal electrode being electrically isolated from the first terminal electrode; at least one heat-generating electrical element having (a) a first metallized contact face, and (b) a second metallized contact face connected to the third terminal electrode, such that a current above a threshold level flowing through the heat-generating electrical element in an electrical circuit including the device generates heat that is transferred directly to the first polymeric positive temperature coefficient resistor to aid tripping to a high resistance state, characterised in that the device further comprises: a first electrode layer formed at the first major surface and in intimate electrical contact therewith, the first terminal electrode being in electrical connection with the first electrode layer; a second terminal electrode being in electrical connection with the second electrode layer, the third terminal electrode being electrically isolated from the second terminal electrode (24, 22); and a generally box-shaped heat-generating element carrier (31, 72, 29) comprising the central planar layer, wherein the element carrier defines a space for receiving the at least one heat-generating electrical element, wherein the second metallized contact face is connected to the third terminal electrode by an electrical interconnect structure, wherein the first metallized contact face is bonded to a part of the first electrode layer arranged to receive the heat-generating electrical element, and wherein the first, second and third terminal electrodes (22, 24, 26) are formed along one or more major edge walls of the device for enabling surface mounting and electrical connection of the device to an electrical circuit substrate. a central planar layer forming a first polymeric positive temperature coefficient resistor having first and second major surfaces, a second electrode layer formed at the second major surface and in intimate electrical contact therewith; and first and third terminal electrodes (24, 26), the third terminal electrode being electrically isolated from the first terminal electrode; at least one heat-generating electrical element having (a) a first metallized contact face, and (b) a second metallized contact face connected to the third terminal electrode, such that a current above a threshold level flowing through the heat-generating electrical element in an electrical circuit including the device generates heat that is transferred directly to the first polymeric positive temperature coefficient resistor to aid tripping to a high resistance state, characterised in that the device further comprises: a first electrode layer formed at the first major surface and in intimate electrical contact therewith, the first terminal electrode being in electrical connection with the first electrode layer; a second terminal electrode being in electrical connection with the second electrode layer, the third terminal electrode being electrically isolated from the second terminal electrode (24, 22); and a generally box-shaped heat-generating element carrier (31, 72, 29) comprising the central planar layer, wherein the element carrier defines a space for receiving the at least one heat-generating electrical element, wherein the second metallized contact face is connected to the third terminal electrode by an electrical interconnect structure, wherein the first metallized contact face is bonded to a part of the first electrode layer arranged to receive the heat-generating electrical element, and wherein the first, second and third terminal electrodes (22, 24, 26) are formed along one or more major edge walls of the device for enabling surface mounting and electrical connection of the device to an electrical circuit substrate. a first electrode layer formed at the first major surface and in intimate electrical contact therewith, the first terminal electrode being in electrical connection with the first electrode layer; a second terminal electrode being in electrical connection with the second electrode layer, the third terminal electrode being electrically isolated from the second terminal electrode (24, 22); and a generally box-shaped heat-generating element carrier (31, 72, 29) comprising the central planar layer, wherein the element carrier defines a space for receiving the at least one heat-generating electrical element, wherein the second metallized contact face is connected to the third terminal electrode by an electrical interconnect structure, wherein the first metallized contact face is bonded to a part of the first electrode layer arranged to receive the heat-generating electrical element, and wherein the first, second and third terminal electrodes (22, 24, 26) are formed along one or more major edge walls of the device for enabling surface mounting and electrical connection of the device to an electrical circuit substrate.