The work is dedicated to investigation of carrier dynamics in SiC, GaN and diamond by using light-induced transient gratings, differential transmittivity, differential reflectivity and photo-luminescence techniques. New absorption coefficient measurement and carrier lifetime microscopy techniques are presented. The experimental studies were performed in a wide range of excess carrier densities and temperatures under single- and two- photon excitation conditions. Strong diffusion coefficient temperature and injection dependences were explained by phonon scattering, inter-carrier interaction processes and degeneracy. In indirect-gap SiC and diamond semiconductors at low injections lifetime was limited by point and surface defects, while in GaN recombination on grain boundaries prevailed. Nonlinear Auger recombination coefficient was observed. It was Coulomb enhanced at low injections and screened at high ones. Radiative recombination coefficient reduced with injection in GaN, while in SiC it was injection independent. Compensating defect concentrations and activation energies were determined from their absorption saturation and recovery rate temperature dependences.