We present a summary of advances in characterization techniques allowing for comprehensive study of physical processes in semiconductor lasers. 5. Electrical and optical measurements of RF modulation response below threshold. 5.1. Determination of the differential carrier lifetime from the device impedance. 5.2. Determination of the differential carrier lifetime from the optical response measurements. 6. Optical measurements of RF modulation response and RIN above threshold 6.1. Determination of the resonant frequency and damping factor using carrier subtraction technique. Determination of the differential gain and the gain compression coefficient. 6.2. Determination of the resonant frequency and differential gain from the RIN measurements. 7. Measurements of the linewidth enhancement factor. 7.1. Measurements of linewidth enhancement factorfrom ASE and TSE spectra. 8. Measurements of the carrier temperature and carrier heating in semiconductor lasers. 8.1. Determination of carrier heating from wavelength chirp and TSE measurements. 9. References.