A semiconductor device includes a laterally extending semiconductor base (82, 96), a buffer (83) adjacent the base and having a first conductivity type dopant, and a laterally extending emitter (85) adjacent the buffer and opposite the base and having a second conductivity type dopant. The buffer (83) is thin and has a fist conductivity type dopant concentration greater than a second conductivity type dopant concentration in adjacent emitter portions to provide a negative temperature coefficient for current gain and a positive temperature coefficient for forward voltage for the device. The buffer may be silicon or germanium. A low temperature bonded interface (103) may be between the emitter and the buffer or the buffer and the base. Another embodiment of a device may include a laterally extending localized lifetime killing portion (92, 102) between oppositely doped first and second laterally extending portions. The localized lifetime killing portion may comprise a plurality of laterally confined and laterally space apart lifetime killing regions. Another device may include one or more PN junctions.