Currently available semiconductor lasers for spectroscopy in the near- and mid-infrared region based on direct band-to-band transitions as gallium-arsenide, indium-phosphide, antimonides and lead-salt containing compounds will be discussed together with the main features of different tunable diode-laser absorption spectrometers for trace gas analysis. Measurements of atmospheric carbon dioxide with a room-temperature 2 microm indium-phosphide laser, applications of antimonide lasers for methane and formaldehyde sensing in the 3-4 microm range and a fast chemical sensor for methane flux measurements based on lead-salt diode-lasers operating near 7.8 microm will be presented.