Polycrystalline silicon (poly‐Si) thin films having large grain size have been obtained by XeCl excimer laser annealing of a‐Si deposited by plasma enhanced chemical vapor deposition on SiNx. The grain size of poly‐Si reaches to about 300 nm with excimer laser irradiation around 500 mJ/cm2. For excimer laser irradiation from 500 to 600 mJ/cm2, instead of further enlargement of grains, amorphous regions appear and increase in the grains. Most of the Si layer becomes an amorphous state at pulse energy density over 600 mJ/cm2. On the other hand, impurity implantation to a‐Si layers using non‐mass‐separated ion doping equipment and a subsequent activation step with excimer laser irradiation enable us to obtain recrystallized poly‐Si layers having low resistivity. By using ion doping and excimer laser annealing, we have obtained excellent n‐channel thin film transistors, the field effect mobility in excess of 40 cm2/V s and the ON/OFF current ratio of more than 106, respectively.