High power diode lasers in mid-infrared spectral range have growing demand for a variety of applications including biological spectral analysis, remote sensing, medical diagnostic tools, and surgery instruments. The work presented in this book focuses on GaSb/AlGaAsSb/GaInAsSb material system for type-I diode lasers at the wavelength range above 3 ?m. 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 QWs and the neighboring layers. 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 ?m; 190 mW at 3.1 ?m; 165 mW at 3.2 ?m; 50 mW at 3.3 ?m; 16 W at 3.4 ?m.