The femtosecond laser (800 nm, 50 fs, 1 kHz) induced damages in Si wafer and fused silica are studied by experiments. The morphologies of structural changes in the two inorganic silicon materials have been investigated by means of charge coupled device (CCD) camera and scanning electron microscopy (SEM). Furthermore, the relationship of damage threshold to laser pulse duration and photon energy is studied. The main process during laser-induced damage in Si wafer is that avalanche ionization which is seeded by electrons due to defects, while that avalanche ionization is seeded by electrons excited by multi-photon ionization is the main process during laser-induced damage in fused silica. The energy deposition is initiated by multiphoton ionization rather than impurities or defects to start an electron avalanche in transparent materials.