There is provided a method by which lightly doped drain (LDD) regions can be formed easily and at good yields in source/drain regions in thin film transistors possessing gate electrodes covered with an oxide covering. A lightly doped drain (LDD) region is formed by introducing an impurity into an island-shaped silicon film in a self-aligning manner, with a gate electrode serving as a mask. First, low-concentration impurity regions are formed in the island-shaped silicon film by using rotation-tilt ion implantation to effect ion doping from an oblique direction relative to the substrate. Low-concentration impurity regions are also formed below the gate electrode at this time. After that, an impurity at a high concentration is introduced normally to the substrate, so forming high-concentration impurity regions. In the above process, a low-concentration impurity region remains below the gate electrode and constitutes a lightly doped drain region.