The ultimate goal of the research is the development of the semiconductor lasers operating at room temperature under continuous wave regime at 3 μm and above. This dissertation focuses on room temperature operated GaSb-based type-I diode lasers. The new device design was proposed to reach desirable laser operation wavelength. Besides employing the compressively strained quantum wells (QWs) in the devices active region, the composition of waveguide and barrier material has been modified to optimize the band offsets between quantum wells and the neighboring layers. The use of quinternary AlGaInAsSb alloys for waveguide and barrier layers, leads to the reduction of conduction band offset and the increase of valence band offset between barrier and QWs in the device active region. The comprehensive study of the characteristics of the devices with different waveguide widths, compositions, and the number of QWs allows us to design and fabricate GaSb-based type-I lasers with world record performance. At room temperature in continuous wave (CW) mode, devices provide 360 mW at 3.0 μm; 190 mW at 3.1 μm; 165 mW at 3.2 μm; 50 mW at 3.3 μm; 16 mW at 3.4 μm.