The longest wavelength III-V semiconductor laser to date has been realized employing a quantum cascade configuration for the active material. It operates at lambda similar to 19 mu m on interminiband transitions in graded superlattices. The waveguide is based on surface plasmon modes confined at a metal-semiconductor interface. The devices emit peak output powers of 14 mW per facet at 10 K and laser action is achieved up to the maximum temperature of 145 K. (C) 2000 American Institute of Physics. [S0003-6951(00)02341-X].