The multi‐shot evolution of laser‐induced periodic structure was studied by the time‐resolved optical diffraction and reflection from the surface of polycrystalline silicon‐on‐insulator during the accumulation of 20 ns ruby laser pulses. In contrast to the results previously reported for the bulk sample, it was observed that the channel of the periodic structure development changed during the multiple irradiations even with a fixed fluence. The observed change occurs because the energy absorption is enhanced by the presence of the periodic structure preformed by the preceding pulses, and the absorbed laser energy at the polycrystalline layer is insulated by the underlying SiO2layer. A previously unappreciated dip structure was observed in the time‐resolved diffraction and a possible explanation is suggested postulating the preferential energy deposition in the valleys of the periodic structure.